http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, 2014; 27(13): 1343–1347 ! 2014 Informa UK Ltd. DOI: 10.3109/14767058.2013.858317
ORIGINAL ARTICLE
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
Assessment of bone health in preterm infants through quantitative ultrasound and biochemical markers Martina Betto1, Paola Gaio1, Ilaria Ferrini1, Francesca De Terlizzi2, Marta Zambolin1, Samuela Scattolin1, Alessandra Pasinato1, and Giovanna Verlato1 1
Women’s and Children’s Health Department, University of Padova, Padova, Italy and 2Laboratory of Clinical Biophysics, Carpi, Modena, Italy
Abstract
Keywords
Objective: To assess bone status in preterm infants with quantitative ultrasound and to search for biochemical markers of bone health. Methods: Metacarpus bone transmission time (mcBTT) was prospectively performed during hospitalization, together with biochemical and clinical outcomes analysis. Results: 154 patients were studied. At 3rd week of life mcBTT positively correlated with serum phosphate. Urinary excretion of calcium and phosphate were assessed in a subgroup of 55 patients: on day 21 mcBTT positively correlated with phosphaturia, negatively with calciuria. Gestational age (GA), weight and length at 3rd week and at 36 weeks of GA correlated positively with mcBTT. We found negative correlation between mcBTT at 3rd week and days of parenteral nutrition, mechanical ventilation period and days to reach 1800 g. Conclusions: Serum phosphate, phosphaturia and calciuria correlate most with mcBTT. Further studies are necessary to verify the possible influence of early bone status on future bone health.
Metabolic bone disease, preterm infants, quantitative ultrasound, serum phosphate
Introduction Preterm infants are at risk of developing not only growth retardation, but also metabolic bone disease (MBD). This condition is an inevitable consequence of common illnesses, metabolic acidosis, use of diuretics and steroids, immobilization, malnutrition, prolonged use of total parenteral nutrition (TPN), insufficient intakes of calcium, phosphorus, vitamin D [1], energy and proteins [2]. Bone mineralization occurs in particular during the last trimester of gestation; then, after birth, there is a rapid reduction in bone density followed by a stabilization that lasts to the end of the first year of life. The decrease of physical density is mostly due to an increase in marrow cavity size, which is faster than the increase in thickness of the bone cortex [3]. Disruption in maternal mineral supply, change in hormonal status and reduction in mechanical stress due to kicks against the uterine wall could lead to decreased bone development [4]. Using dual X-ray absorptiometry technology (DEXA), Rigo et al. have shown that in very low birth weight (VLBW) infants remodeling process of bone occurs earlier than in term babies causing increased bone fragility and higher fracture risk [4,5]. Both osteopenia, resulting from diminished synthesis and/or increased resorption of organic bone Address for correspondence: Giovanna Verlato, MD, PhD, Women’s and Children’s Health Department, University of Padova, Via Giustiniani 3, 35128 Padova, Italy. Tel: 39 49 821 1490. Fax 39 49 821 3238. E-mail: [email protected]
History Received 3 May 2013 Accepted 20 October 2013 Published online 26 November 2013
matrix, and osteomalacia/rickets due to a deficient supply or uptake of mineral, can occur after premature birth [3], in a condition called MBD. MBD occurs in 39% of preterm infants with a birth weight under 1500 g and fractures are reported in 10.5% of this population [6]. Furthermore, in the long-term MBD might adversely affect linear growth and childhood height [7]. Adequate administration of minerals, vitamin D, energy and proteins, associated with physical therapy, could reduce the prevalence and severity of MBD. Analyzing bone status in preterms remains difficult: X-rays are not reliable at diagnosing bone disease due to the subjective interpretation, in particular in the absence of significant demineralization or fractures; DEXA involves radiations, the device is not portable and sedation could be required. Quantitative ultrasound (QUS) is a simpler, noninvasive, low-cost, non-ionizing method and it can be used at the bedside. Serum and urinary parameters of bone metabolism, associated with imaging techniques, could be useful to identify preterm infants at risk of developing MBD. Some authors have shown correlations between radiological exams and serum alkaline phosphatase, serum phosphate and urinary excretion of calcium [8]. The aim of our study was to assess bone status in preterm infants 31 GA in parenteral nutrition, using QUS, and to investigate which biochemical or clinical factors could be related to improved ultrasound parameters (mcBTT)
1344
M. Betto et al.
and could be considered as markers of bone development in preterm infants.
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
Methods For our study, we enrolled preterm infants 31 GA, in parenteral nutrition since 48 h of life, hospitalized in the neonatal intensive care unit at the Department of Pediatrics of the University of Padova (Italy) from May 2009 to January 2012. Exclusion criteria were: major malformations, congenital infections and metabolic disorders. Informed consent was obtained from parents before the study enrollment. All patients received a progressive TPN regimen through a central umbilical or percutaneous catheter. Intravenous micro and macronutrients were supplied according to the ESPGHAN guidelines [9] and according to our unit protocol [2]. In particular, amino acids supplementation was started at 1.5 g/kg per day and advanced from 0.5 g/kg per day to a maximum of 4 g/kg per day; calcium and phosphorus intake were between 0.8 and 2 mmol/kg per day, modulated to keep serum levels between 2–2.5 mmol/l and 1.8–2.6 mmol/l, respectively. Parenteral magnesium and vitamin D administration were 0.2 mmol/kg per day and 30 UI/kg per day, respectively. Patients received minimal enteral feeding (12–24 ml/kg per day) during the first week of life. Then, in the absence of contraindications, feedings were advanced (with human milk or formula) at a rate of 10–20 ml/kg per day; human milk was fortified (FM 85Õ , Nestle, Italian SPA, Milan, Italy) when an intake of 100 ml/kg was reached. As feeding advanced, TPN was decreased and stopped when enteral feeding reached 100–120 ml/kg per day. Growth was assessed through anthropometric measures. We registered daily weight, weekly total length and head circumference from birth to discharge and we considered days to reach 1800 g. QUS was performed with DMB Sonic BONE PROFILERÕ (IGEA, Carpi, Modena, Italy) to assess bone status within 24 h from birth, at 3rd week of life and at 36 weeks of GA. QUS uses two coaxial probes, one emitting and one receiving, mounted on a calliper. The device measures the distance between the probes and the time elapsing between emission and reception to calculate two parameters: metacarpus speed of sound (mcSOS) and metacarpus bone transmission time (mcBTT). It requires four measures for every patient, with a tolerated range of 10 m/s for SOS. The sensibility was 0.01 mm for distance and 0.05 ms for time, with a tolerated range of 10 m/s. The device provides mcBTT standard deviation score using published growth charts for preterm infants [10]. To evaluate density, elasticity and bone structure, we tested mcBTT that minimizes the confounding effect of soft tissue [10,11]. Bone metabolism was assessed through serum calcium, phosphate, magnesium and alkaline phosphatase at birth and on day 21. At least once a day, a blood sample was drawn to determine serum pH and base excess (BE) during the first week of life. Due to preliminary results on mcBTT deflection on day 21 we decided to perform urine analysis in the more recently enrolled patients (n ¼ 55). We therefore collected 6 h urine samples through an adhesive bag, at birth and on day 21. Urinary creatinine, calcium and phosphorus of every sample
J Matern Fetal Neonatal Med, 2014; 27(13): 1343–1347
were analyzed to determine urinary calcium (UCa/UCr) and phosphate (UPO4/UCr) creatinine ratios (Modular DPÕ – Roche Diagnostics, Mannheim, Germany). A close linear correlation between 24-h urinary calcium excretion and random UCa/Cr ratio was established in children [12]. We also recorded clinical outcomes such as: mechanical ventilation period, TPN period and days to reach 1800 g. SPSS 15.0Õ (SPSS Inc, Chicago, IL) and Microsoft Office Excel 2010Õ (Microsoft Corporation, Redmond, WA) were used for statistical analysis. Data were expressed as mean standard deviation. Pearson’s correlation was used to analyze the relationships between variables. Significance was set at p50.05.
Results The study was carried out in 154 patients hospitalized in our neonatal intensive care unit from May 2009 to January 2012. In this population 45% were males and 55% females. Mean GA was 27.54 1.97 weeks (from 23.0 to 31.0 GA) and mean birth weight was 902.83 g 216.06 g (from 420 to 1250 g). Clinical and anthropometric parameters during the hospitalization are shown in Table 1; QUS measures are shown in Table 1. We observed a deflection of mcBTT from birth (0.40 0.12 ms) to 3rd week of life (0.38 0.09 ms, p40.05) followed by an increase of this parameter during the first months of life (0.44 0.07 ms at 36 GA, p50.01 versus birth, p50.001 versus 3rd week of life). Considering Z-score mcBTT (using published growth charts for newborns [10]), we observed that at 36 week of GA, 68% of newborns had a Z-score 52 SD (compared to 21% of newborns at birth). We found a positive correlation at 3rd week of life, between mcBTT and mean serum phosphate (r ¼ 0.37; p ¼ 0.00); on the other hand no correlations were found between mcBTT and ALP (r ¼ 0.06; p ¼ 0.51) or serum calcium (r ¼ 0.12; p ¼ 0.24) (Table 2) and other plasma biochemical parameters. We found a positive correlation between mcBTT at 3rd week and the mean BE during the first week of life (r ¼ 0.22; p ¼ 0.00) (Table 2). Table 1. Clinical, anthropometric parameters and QUS measures during hospitalization. Mean s.d Gestational age (weeks) Birth weight (g) Length at birth (cm) Head circumference at birth (cm) APGAR at 5 minute Weight, 21 days (g) Length, 21 days (cm) Head circumference, 21 days(cm) Weight at 36wks of GA (g) Length at 36wks of GA (g) Head circumference at 36wks of GA(g) Days to reach 1800 g TPN period (days) Mechanical ventilation period (days) Basal mcSOS (m/s) Basal mcBTT (ms) mcSOS, 3rd week of life (m/s) mcBTT 3rd week of life (ms) mcSOS at 36 wks of GA (m/s) mcBTT at 36 wks of GA (ms)
27.54 1.97 902.83 216.06 35.16 4.94 24.88 2.08 7.88 1.20 989.12 268.33 36.28 4.59 26.54 2.33 1823.79 324.97 42.19 2.57 30.66 1.74 58.07 19.93 27.49 15.31 6.48 10.91 1642.17 28.35 0.40 0.12 1623.80 23.52 0.38 0.09 1614.84 17.44 0.44 0.07
Quantitative ultrasound in preterm infants
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
DOI: 10.3109/14767058.2013.858317
In a subgroup of 55 patients we assessed urinary excretion of calcium and phosphate. McBTT at 3rd week of life positively correlated with UPO4/UCr (r ¼ 0.34; p ¼ 0.01) and inversely correlated with UCa/UCr (r ¼ 0.28; p ¼ 0.03) (Table 2). UPO4/UCr on day 21 also correlated with mcBTT at 36 weeks of GA (r ¼ 0.24; p ¼ 0.00) (data not shown). We observed a direct correlation between urinary excretion of phosphate and serum phosphate (r ¼ 0.40; p ¼ 0.01), and an inverse correlation between urinary excretion of calcium and the mean BE of the first week of life (r ¼ 0.35; p ¼ 0.01) (data not shown). Some anthropometric parameters correlated positively with the measures of mcBTT obtained during the study (Table 3). In particular, mcBTT at 3rd week of life was related to weight (r ¼ 0.42, p ¼ 0.00) and total length (r ¼ 0.28, p ¼ 0.00) on day 21 and mcBTT at 36 weeks of GA correlated with weight (r ¼ 0.26; p ¼ 0.02) and total length (r ¼ 0.30, p ¼ 0.00) at the same GA. In the end, we considered some clinical quantitative outcomes and we found negative correlation between mcBTT at 3rd week and TPN period (r ¼ 0.30; p ¼ 0.00), mechanical ventilation period (r ¼ 0.21; p ¼ 0.01) and days to reach 1800 g (r ¼ 0.31; p ¼ 0.00) (Table 3).
Discussion In our study, we assessed bone health using QUS and we investigated possible markers of bone development in preterm infants. Table 2. Correlation between mcBTT and serum and urinary values. mcBTT, 3rd wk of life Pearson’s correlation Mean base excess 1st week (mean 6.14 2.14) Ca, 21 days (mean 2.54 0.14 mmol/l) P, 21 days (mean 1.78 0.42 mmol/l) ALP, 21 days (mean 409.97 129.93 UI/l) UCa/UCr, 21 days (mean 1.99 1.00 mmol/mmol) UPO4/UCr, 21 days (mean 8.50 6.21 mmol/mmol)
Sig. (two tailed)
0.22
0.00
0.12
0.24
0.37
0.00
0.06
0.51
0.28
0.03
0.34
0.01
QUS measures both qualitative and quantitative bone properties, considering not only mineral content, but also organic matrix, so it could be used to estimate bone status [13]. In clinical practice this method could identify premature newborns at high risk to develop MBD. In our study we chose to use mcBTT to minimize the confounding effect of soft tissue [10,11]. In other similar studies another parameter such as SOS has been used, but Bajaj et al. have shown that this parameter could be altered in vivo and in vitro by soft and fat tissues, edema, birth weight and age of life [14]. We compared ultrasound results to Ritschl’s curves, based on term and preterm QUS data [10] and we also showed a direct correlation between anthropometric parameters at birth and basal mcBTT (Table 3); furthermore, the same anthropometric parameters correlated with longitudinal mcBTT measures during hospitalization (on day 21 and at 36 weeks of GA). First of all we observed that the highest correlation of mcBTT at birth is with birthweight indicating that fetal growth is the most relevant factor influencing bone development. These correlation coefficients are not so high with respect to other results reported in the literature [10], mainly due to the fact that in the previous studies the range of GA considered in the analyses were larger and the mcBTT increase was consequently larger in comparison with the precision of the measurement. Ritschl’s reference curves for preterm newborns describe a postnatal decrease of mcSOS (as in term infants) with a lower nadir that is reached earlier in comparison to term infants; mcBTT values, instead, increase after birth, however changes are not as fast as those observed during in utero growth. In our study we observed the same deflection of mcSOS, but a different change occurring in mcBTT, that decreases during the first three weeks of life followed by an increase over time and this trend convinced us to perform urine analysis in the successive enrolled patients. We observed a positive correlation between mcBTT at 3rd week and the mean BE during the first week of life (r ¼ 0.22; p ¼ 0.00) (Table 2) and a negative correlation between mean BE during the first week of life and UCa/UCr on day 21 (r ¼ 0.35; p ¼ 0.01) (data not shown). This suggested us a role of metabolic acidosis during the first week of life on bone status of our population that could explain mcBTT deflection. Acidosis increased renal calcium excretion in a group of preterm
Bold values show statistical significance with p-value50.05. Table 3. Correlation between mcBTT and anthropometric and clinical parameters. Basal mcBTT
Gestational age Birth weight Length at birth Weight, 21 days Weight, 36 wk of GA Length, 21 days Length, 36 wk of GA Day to reach 1800 g TPN period Mechanical ventilation period
mcBTT, 3rd wk of life
mcBTT at 36 wk of GA
Pearson’s correlation
Sig. (two tailed)
Pearson’s correlation
Sig. (two tailed)
Pearson’s correlation
Sig. (two tailed)
0.23 0.40 0.20 0.40 0.34 0.19 0.29 – – –
0.00 0.00 0.02 0.00 0.00 0.04 0.00 – – –
0.30 0.43 0.17 0.42 0.19 0.28 0.26 0.31 0.30 0.21
0.00 0.00 0.03 0.00 0.03 0.00 0.00 0.00 0.00 0.01
0.23 0.30 0.02 0.32 0.26 0.17 0.30 0.30 0.05 0.24
0.01 0.00 0.77 0.00 0.00 0.11 0.00 0.00 0.60 0.00
Bold values show statistical significance with p-value50.05.
1345
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
1346
M. Betto et al.
infants, causing physiochemical dissolution with net alkali release from bone [15]. We evaluated biochemical parameters that could be markers of bone status, and their relationship with ultrasound parameters; some studies had already investigated this topic but with conflicting results. Using DEXA in preterm newborns, Backstrom et al. showed that the combination of ALP 4900 IU/L and phosphate 51.8 mmol/L could be a screening test for low mineral density [16] but correlations between bone mineral content obtained by DEXA and ALP or serum phosphate were not confirmed in Faerk’s study [17]. Catache et al. compared biochemical parameters with radiological signs of mineral deficiency and suggested the role of urinary levels of calcium in the early detection of demineralization, even if X-ray is not the method of choice for the early diagnosis of MBD [18]. Some studies investigated these topics with QUS method and negative correlations between ALP and tibial SOS were detected [19,20]; mean tibial SOS Z-score of infants with ALP 900 IU/L was significantly lower than that of the infants with ALP5900 UI/ L in Altuncu’s study [21]. A recent study, confirmed an inverse correlation between QUS measurements and ALP in a population of preterm and term infants but there was no correlation of altered QUS measurements over time with calcium and phosphate concentrations in urine and serum [22]. However, in the same study there was a highly significant inverse correlation of ALP with phosphate concentration in urine suggesting that lower phosphaturia is a marker of worsening bone status. In our study, we observed a direct correlation between mcBTT at 3rd week and serum phosphate on day 21, but not with ALP on day 21, as in other studies [23]. ALP is used as a marker of bone metabolism, but this value is the sum of three isoforms (liver, intestine and bone); even if bone isoform contributes to a large proportion of serum ALP, role of the other isoforms have to be considered in infants with gastrointestinal or hepatic disease [24]. In fact, we enrolled preterm infants needing parenteral nutrition at high risk to develop intolerance to enteral nutrition and cholestasis; for these reasons total ALP could not have been correlated to mcBTT. In a subgroup of patients, mcBTT at 3rd week positively correlated with urinary excretion of phosphate (r ¼ 0.34; p ¼ 0.01) and negatively correlated with urinary excretion of calcium (r ¼ 0.28; p ¼ 0.03): decreasing of UPO4/UCr and increasing of UCa/UCr could be a sign of worsening bone metabolism. It is interesting to underline that urinary excretion of phosphate on day 21 also positively correlated with mcBTT at 36 weeks of GA (r ¼ 0.24; p ¼ 0.00). Aladangady et al. assessed urinary calcium and phosphate creatinine ratios in a population of premature infants between 24 and 34 GA: patients in parenteral nutrition had higher UCa/UCr and lower UPO4/UCr, showing decreased utilization of calcium for bone growth due to phosphate depletion and lower protein intake [12]. We observed a direct correlation between urinary excretion of phosphate and serum phosphate (r ¼ 0.40; p ¼ 0.01), so we could confirm that neonates with phosphate depletion have a lower phosphaturia and a worsened mcBTT. These results suggest the use of urinary parameters as screening test to assess bone status.
J Matern Fetal Neonatal Med, 2014; 27(13): 1343–1347
A limit of our results could be that the r values are small suggesting that a greater part of the variance is not explained even though the analyzed parameters are statistically significant. Nonetheless, we want to outline that the sensitivity of the mcBTT measurement is sufficiently high to reveal the influence of metabolic factors on the mcBTT variations, indicating that this parameter can identify particular changes in the bone tissue related to metabolic effects. The negative correlations between mcBTT at 3rd week and TPN period, mechanical ventilation period and days to reach 1800 g, reflect the influence of clinical status of ill neonates on bone metabolism. In particular, the use of TPN is associated with MBD and the etiology is likely multifactorial: inadequate supply of proteins and energy could compromise the synthesis of bone tissue [4]; the amount of calcium and phosphate supplied by TPN could be inadequate to match the in utero mineral accretion rates and it could depend on the solubility of the pharmacological preparations and to the restriction of fluids intake. Moreover, other clinical conditions related to TPN may influence bone status, e.g. gastrointestinal and liver diseases, effect of hormones and renal control, immobilization, therapy with drug-induced alteration in bone metabolism and lack of enteral nutrition [25]. Enteral nutrition is more physiological and preterm formulas actually in use and fortification of human milk have improved minerals and proteins intakes in premature infants. Ventilation period seems to play a key role in the development of MBD, possibly due to concomitant immobilization; mechanical factors and muscle activities play a part in improving bone growth [26,27], so, during inactivity the bones could get weaker [3] and this could explain the negative correlation between days of mechanical ventilation and mcBTT. In conclusion, in our study, serum phosphate correlates most with ultrasound parameters of bone status (mcBTT). Low urinary excretion of phosphate, high urinary excretion of calcium and low serum phosphate could be regarded as early markers of inadequate bone development. QUS may have a significant role in monitoring bone health in preterm infant. We know that bone health in the analyzed preterm babies is not completely explained by the variables investigated in the present study. Further studies, including a larger number of infants, and a long-term follow-up, could help us in better understanding which are the variables more linked to bone growth and the possible influence of early bone status in future bone health.
Declaration of interest The authors report no conflicts of interest and have nothing to disclose.
References 1. Ryan S. Nutritional aspects of metabolic bone disease in the newborn. Arch Dis Child 1996;74:F145–8. 2. Scattolin S, Gaio P, Betto M, et al. Parenteral amino acid intakes: possible influences of higher intakes on growth and bone status in preterm infants. J Perinatol 2013;33:33–9. 3. Rauch F, Schoenau E. Skeletal development in premature infants: a review of bone physiology beyond nutritional aspects. Arch Dis Child Fetal Neonatal Ed 2002;86:F82–5. 4. Rigo J, Senterre J. Nutritional needs of premature infants: current issues. J Pediatr 2006;149:s80–8.
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
DOI: 10.3109/14767058.2013.858317
5. Rigo J, Nyamugabo K, Picaud JC, et al. Reference values of body composition obtained by dual energy X-ray absorptiometry in preterm and term neonates. J Pediatr Gastroenterol Nutr 1998;27: 184–90. 6. Dabezies EJ, Warren PD. Fractures in very low birth weight infants with rickets. Clin Orthop Relat Res 1997;335:233–9. 7. Fewtrell MS, Cole TJ, Bishop NJ, Lucas A. Neonatal factors predicting childhood height in preterm infants: evidence for a persisting effect of early metabolic one disease? J Pediatr 2000;137: 668–73. 8. Visser F, Spij AJ, Brus F. The validity of biochemical markers in metabolic bone disease in preterm infants: a systematic review. Acta Paediatr 2012:101:562–8. 9. Koletzko B, Goulet O, Hunt J, et al. Guidelines on Paediatric Parenteral Nutrition of the European Society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) and the European Society for Clinical Nutrition and Metabolism (ESPEN), supported by the European Society of Paediatric Research (ESPR). J Pediatr Gastroenterol Nutr 2005;41:S1–87. 10. Ritschl E, Wehmeijer K, De Terlizzi F, et al. Assessment of skeletal development in preterm and term infants by Quantitative Ultrasound. Pediatr Res 2005;58:1–7. 11. Rubinacci A, Moro GE, Boehm G, et al. Quantitative ultrasound for the assessment of osteopenia in preterm infants. Eur J Endocrinol 2003;149:307–15. 12. Aladangady N, Coen PG, White MP, et al. Urinary excretion of calcium and phosphate in preterm infants. Pediatr Nephrol 2004;19: 1225–31. 13. DeTerlizzi F, Battista S, Cavani F, et al. Influence of bone tissue density and elasticity on ultrasound propagation: an in vitro study. J Bone Mineral Res 2000;15:2458–66. 14. Bajaj M, Koo W, Hammami M, Hockman EM. Effect of subcutaneous fat on quantitative bone ultrasound in chicken and neonates. Pediatr Res 2010;68:81–3. 15. Kalhoff H, Diekmann L, Rudloff S, Manz F. Renal excretion of calcium and phosphorus in premature infants with incipient late metabolic acidosis. J Pediatr Gastroenter Nutr 2001;33:565–9.
Quantitative ultrasound in preterm infants
1347
16. Backstrom MC, Kouri T, Kuusela AL, et al. Bone isoenzyme of serum alkaline phosphatase and serum inorganic phosphate in metabolic bone disease of prematurity. Acta Paediatr 2000;89: 867–73. 17. Faerk J, Peitersen B, Petersen S, Michaelsen KF. Bone mineralisation in premature infants cannot e predicted from serum alkaline phosphatase or serum phosphate. Arch Dis Child Fetal Neonatal Ed 2002;87:F133–6. 18. Catache M, Leone CR. Role of plasma and urinary calcium and phosphorus measurements in early detection of phosphorus deficiency in very low birthweight infants. Acta Paediatr 2003;92: 76–80. 19. Tomlinson C, McDevitt H, Ahmed SF, White MP. Longitudinal changes in bone health as assessed by the speed of sound in very low birth weight infants. J Pediatr 2006;148:450–5. 20. Nemet D, Dolfin T, Wolach B, Eliakim A. Quantitative ultrasound measurements of bone speed of sound in premature infants. Eur J Pediatr 2001;160:736–40. 21. Altuncu E, Akman I, Yurdakul Z, et al. Quantitative ultrasound and biochemical parameters for the assessment of osteopenia in preterm infants. J Matern Fetal Neonatal Med 2007;20:401–5. 22. Rack B, Lochmu¨ller E-M, Janni W, et al. Ultrasound for the assessment of bone quality in preterm and term infants. J Perinatol 2012;32:218–26. 23. Fewtrell MS, Loh KL, Chomtho S, et al. Quantitative ultrasound (QUS): a useful tool for monitoring bone health in preterm infants? Acta Paediatr 2008;97:1625–30. 24. McDevitt H, Ahmed SF. Quantitative ultrasound assessment of bone health in the neonate. Neonatology 2007;91:2–11. 25. Klein GL. Metabolic bone disease of total parenteral nutrition. Nutrition 1998;14:149–52. 26. Moyer-Mileur LJ, Ball SD, Brunstetter VL, Chan GM. Maternaladministered physical activity enhances bone mineral acquisition in premature very low birth weight infants. J Perinatol 2008;28:432–7. 27. Vignochi CM, Silveira RC, Miura E, et al. Physical therapy reduces bone resorption and increased bone formation in preterm infants. Am J Perinatol 2012;29:573–8.
ORIGINAL ARTICLE
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
Assessment of bone health in preterm infants through quantitative ultrasound and biochemical markers Martina Betto1, Paola Gaio1, Ilaria Ferrini1, Francesca De Terlizzi2, Marta Zambolin1, Samuela Scattolin1, Alessandra Pasinato1, and Giovanna Verlato1 1
Women’s and Children’s Health Department, University of Padova, Padova, Italy and 2Laboratory of Clinical Biophysics, Carpi, Modena, Italy
Abstract
Keywords
Objective: To assess bone status in preterm infants with quantitative ultrasound and to search for biochemical markers of bone health. Methods: Metacarpus bone transmission time (mcBTT) was prospectively performed during hospitalization, together with biochemical and clinical outcomes analysis. Results: 154 patients were studied. At 3rd week of life mcBTT positively correlated with serum phosphate. Urinary excretion of calcium and phosphate were assessed in a subgroup of 55 patients: on day 21 mcBTT positively correlated with phosphaturia, negatively with calciuria. Gestational age (GA), weight and length at 3rd week and at 36 weeks of GA correlated positively with mcBTT. We found negative correlation between mcBTT at 3rd week and days of parenteral nutrition, mechanical ventilation period and days to reach 1800 g. Conclusions: Serum phosphate, phosphaturia and calciuria correlate most with mcBTT. Further studies are necessary to verify the possible influence of early bone status on future bone health.
Metabolic bone disease, preterm infants, quantitative ultrasound, serum phosphate
Introduction Preterm infants are at risk of developing not only growth retardation, but also metabolic bone disease (MBD). This condition is an inevitable consequence of common illnesses, metabolic acidosis, use of diuretics and steroids, immobilization, malnutrition, prolonged use of total parenteral nutrition (TPN), insufficient intakes of calcium, phosphorus, vitamin D [1], energy and proteins [2]. Bone mineralization occurs in particular during the last trimester of gestation; then, after birth, there is a rapid reduction in bone density followed by a stabilization that lasts to the end of the first year of life. The decrease of physical density is mostly due to an increase in marrow cavity size, which is faster than the increase in thickness of the bone cortex [3]. Disruption in maternal mineral supply, change in hormonal status and reduction in mechanical stress due to kicks against the uterine wall could lead to decreased bone development [4]. Using dual X-ray absorptiometry technology (DEXA), Rigo et al. have shown that in very low birth weight (VLBW) infants remodeling process of bone occurs earlier than in term babies causing increased bone fragility and higher fracture risk [4,5]. Both osteopenia, resulting from diminished synthesis and/or increased resorption of organic bone Address for correspondence: Giovanna Verlato, MD, PhD, Women’s and Children’s Health Department, University of Padova, Via Giustiniani 3, 35128 Padova, Italy. Tel: 39 49 821 1490. Fax 39 49 821 3238. E-mail: [email protected]
History Received 3 May 2013 Accepted 20 October 2013 Published online 26 November 2013
matrix, and osteomalacia/rickets due to a deficient supply or uptake of mineral, can occur after premature birth [3], in a condition called MBD. MBD occurs in 39% of preterm infants with a birth weight under 1500 g and fractures are reported in 10.5% of this population [6]. Furthermore, in the long-term MBD might adversely affect linear growth and childhood height [7]. Adequate administration of minerals, vitamin D, energy and proteins, associated with physical therapy, could reduce the prevalence and severity of MBD. Analyzing bone status in preterms remains difficult: X-rays are not reliable at diagnosing bone disease due to the subjective interpretation, in particular in the absence of significant demineralization or fractures; DEXA involves radiations, the device is not portable and sedation could be required. Quantitative ultrasound (QUS) is a simpler, noninvasive, low-cost, non-ionizing method and it can be used at the bedside. Serum and urinary parameters of bone metabolism, associated with imaging techniques, could be useful to identify preterm infants at risk of developing MBD. Some authors have shown correlations between radiological exams and serum alkaline phosphatase, serum phosphate and urinary excretion of calcium [8]. The aim of our study was to assess bone status in preterm infants 31 GA in parenteral nutrition, using QUS, and to investigate which biochemical or clinical factors could be related to improved ultrasound parameters (mcBTT)
1344
M. Betto et al.
and could be considered as markers of bone development in preterm infants.
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
Methods For our study, we enrolled preterm infants 31 GA, in parenteral nutrition since 48 h of life, hospitalized in the neonatal intensive care unit at the Department of Pediatrics of the University of Padova (Italy) from May 2009 to January 2012. Exclusion criteria were: major malformations, congenital infections and metabolic disorders. Informed consent was obtained from parents before the study enrollment. All patients received a progressive TPN regimen through a central umbilical or percutaneous catheter. Intravenous micro and macronutrients were supplied according to the ESPGHAN guidelines [9] and according to our unit protocol [2]. In particular, amino acids supplementation was started at 1.5 g/kg per day and advanced from 0.5 g/kg per day to a maximum of 4 g/kg per day; calcium and phosphorus intake were between 0.8 and 2 mmol/kg per day, modulated to keep serum levels between 2–2.5 mmol/l and 1.8–2.6 mmol/l, respectively. Parenteral magnesium and vitamin D administration were 0.2 mmol/kg per day and 30 UI/kg per day, respectively. Patients received minimal enteral feeding (12–24 ml/kg per day) during the first week of life. Then, in the absence of contraindications, feedings were advanced (with human milk or formula) at a rate of 10–20 ml/kg per day; human milk was fortified (FM 85Õ , Nestle, Italian SPA, Milan, Italy) when an intake of 100 ml/kg was reached. As feeding advanced, TPN was decreased and stopped when enteral feeding reached 100–120 ml/kg per day. Growth was assessed through anthropometric measures. We registered daily weight, weekly total length and head circumference from birth to discharge and we considered days to reach 1800 g. QUS was performed with DMB Sonic BONE PROFILERÕ (IGEA, Carpi, Modena, Italy) to assess bone status within 24 h from birth, at 3rd week of life and at 36 weeks of GA. QUS uses two coaxial probes, one emitting and one receiving, mounted on a calliper. The device measures the distance between the probes and the time elapsing between emission and reception to calculate two parameters: metacarpus speed of sound (mcSOS) and metacarpus bone transmission time (mcBTT). It requires four measures for every patient, with a tolerated range of 10 m/s for SOS. The sensibility was 0.01 mm for distance and 0.05 ms for time, with a tolerated range of 10 m/s. The device provides mcBTT standard deviation score using published growth charts for preterm infants [10]. To evaluate density, elasticity and bone structure, we tested mcBTT that minimizes the confounding effect of soft tissue [10,11]. Bone metabolism was assessed through serum calcium, phosphate, magnesium and alkaline phosphatase at birth and on day 21. At least once a day, a blood sample was drawn to determine serum pH and base excess (BE) during the first week of life. Due to preliminary results on mcBTT deflection on day 21 we decided to perform urine analysis in the more recently enrolled patients (n ¼ 55). We therefore collected 6 h urine samples through an adhesive bag, at birth and on day 21. Urinary creatinine, calcium and phosphorus of every sample
J Matern Fetal Neonatal Med, 2014; 27(13): 1343–1347
were analyzed to determine urinary calcium (UCa/UCr) and phosphate (UPO4/UCr) creatinine ratios (Modular DPÕ – Roche Diagnostics, Mannheim, Germany). A close linear correlation between 24-h urinary calcium excretion and random UCa/Cr ratio was established in children [12]. We also recorded clinical outcomes such as: mechanical ventilation period, TPN period and days to reach 1800 g. SPSS 15.0Õ (SPSS Inc, Chicago, IL) and Microsoft Office Excel 2010Õ (Microsoft Corporation, Redmond, WA) were used for statistical analysis. Data were expressed as mean standard deviation. Pearson’s correlation was used to analyze the relationships between variables. Significance was set at p50.05.
Results The study was carried out in 154 patients hospitalized in our neonatal intensive care unit from May 2009 to January 2012. In this population 45% were males and 55% females. Mean GA was 27.54 1.97 weeks (from 23.0 to 31.0 GA) and mean birth weight was 902.83 g 216.06 g (from 420 to 1250 g). Clinical and anthropometric parameters during the hospitalization are shown in Table 1; QUS measures are shown in Table 1. We observed a deflection of mcBTT from birth (0.40 0.12 ms) to 3rd week of life (0.38 0.09 ms, p40.05) followed by an increase of this parameter during the first months of life (0.44 0.07 ms at 36 GA, p50.01 versus birth, p50.001 versus 3rd week of life). Considering Z-score mcBTT (using published growth charts for newborns [10]), we observed that at 36 week of GA, 68% of newborns had a Z-score 52 SD (compared to 21% of newborns at birth). We found a positive correlation at 3rd week of life, between mcBTT and mean serum phosphate (r ¼ 0.37; p ¼ 0.00); on the other hand no correlations were found between mcBTT and ALP (r ¼ 0.06; p ¼ 0.51) or serum calcium (r ¼ 0.12; p ¼ 0.24) (Table 2) and other plasma biochemical parameters. We found a positive correlation between mcBTT at 3rd week and the mean BE during the first week of life (r ¼ 0.22; p ¼ 0.00) (Table 2). Table 1. Clinical, anthropometric parameters and QUS measures during hospitalization. Mean s.d Gestational age (weeks) Birth weight (g) Length at birth (cm) Head circumference at birth (cm) APGAR at 5 minute Weight, 21 days (g) Length, 21 days (cm) Head circumference, 21 days(cm) Weight at 36wks of GA (g) Length at 36wks of GA (g) Head circumference at 36wks of GA(g) Days to reach 1800 g TPN period (days) Mechanical ventilation period (days) Basal mcSOS (m/s) Basal mcBTT (ms) mcSOS, 3rd week of life (m/s) mcBTT 3rd week of life (ms) mcSOS at 36 wks of GA (m/s) mcBTT at 36 wks of GA (ms)
27.54 1.97 902.83 216.06 35.16 4.94 24.88 2.08 7.88 1.20 989.12 268.33 36.28 4.59 26.54 2.33 1823.79 324.97 42.19 2.57 30.66 1.74 58.07 19.93 27.49 15.31 6.48 10.91 1642.17 28.35 0.40 0.12 1623.80 23.52 0.38 0.09 1614.84 17.44 0.44 0.07
Quantitative ultrasound in preterm infants
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
DOI: 10.3109/14767058.2013.858317
In a subgroup of 55 patients we assessed urinary excretion of calcium and phosphate. McBTT at 3rd week of life positively correlated with UPO4/UCr (r ¼ 0.34; p ¼ 0.01) and inversely correlated with UCa/UCr (r ¼ 0.28; p ¼ 0.03) (Table 2). UPO4/UCr on day 21 also correlated with mcBTT at 36 weeks of GA (r ¼ 0.24; p ¼ 0.00) (data not shown). We observed a direct correlation between urinary excretion of phosphate and serum phosphate (r ¼ 0.40; p ¼ 0.01), and an inverse correlation between urinary excretion of calcium and the mean BE of the first week of life (r ¼ 0.35; p ¼ 0.01) (data not shown). Some anthropometric parameters correlated positively with the measures of mcBTT obtained during the study (Table 3). In particular, mcBTT at 3rd week of life was related to weight (r ¼ 0.42, p ¼ 0.00) and total length (r ¼ 0.28, p ¼ 0.00) on day 21 and mcBTT at 36 weeks of GA correlated with weight (r ¼ 0.26; p ¼ 0.02) and total length (r ¼ 0.30, p ¼ 0.00) at the same GA. In the end, we considered some clinical quantitative outcomes and we found negative correlation between mcBTT at 3rd week and TPN period (r ¼ 0.30; p ¼ 0.00), mechanical ventilation period (r ¼ 0.21; p ¼ 0.01) and days to reach 1800 g (r ¼ 0.31; p ¼ 0.00) (Table 3).
Discussion In our study, we assessed bone health using QUS and we investigated possible markers of bone development in preterm infants. Table 2. Correlation between mcBTT and serum and urinary values. mcBTT, 3rd wk of life Pearson’s correlation Mean base excess 1st week (mean 6.14 2.14) Ca, 21 days (mean 2.54 0.14 mmol/l) P, 21 days (mean 1.78 0.42 mmol/l) ALP, 21 days (mean 409.97 129.93 UI/l) UCa/UCr, 21 days (mean 1.99 1.00 mmol/mmol) UPO4/UCr, 21 days (mean 8.50 6.21 mmol/mmol)
Sig. (two tailed)
0.22
0.00
0.12
0.24
0.37
0.00
0.06
0.51
0.28
0.03
0.34
0.01
QUS measures both qualitative and quantitative bone properties, considering not only mineral content, but also organic matrix, so it could be used to estimate bone status [13]. In clinical practice this method could identify premature newborns at high risk to develop MBD. In our study we chose to use mcBTT to minimize the confounding effect of soft tissue [10,11]. In other similar studies another parameter such as SOS has been used, but Bajaj et al. have shown that this parameter could be altered in vivo and in vitro by soft and fat tissues, edema, birth weight and age of life [14]. We compared ultrasound results to Ritschl’s curves, based on term and preterm QUS data [10] and we also showed a direct correlation between anthropometric parameters at birth and basal mcBTT (Table 3); furthermore, the same anthropometric parameters correlated with longitudinal mcBTT measures during hospitalization (on day 21 and at 36 weeks of GA). First of all we observed that the highest correlation of mcBTT at birth is with birthweight indicating that fetal growth is the most relevant factor influencing bone development. These correlation coefficients are not so high with respect to other results reported in the literature [10], mainly due to the fact that in the previous studies the range of GA considered in the analyses were larger and the mcBTT increase was consequently larger in comparison with the precision of the measurement. Ritschl’s reference curves for preterm newborns describe a postnatal decrease of mcSOS (as in term infants) with a lower nadir that is reached earlier in comparison to term infants; mcBTT values, instead, increase after birth, however changes are not as fast as those observed during in utero growth. In our study we observed the same deflection of mcSOS, but a different change occurring in mcBTT, that decreases during the first three weeks of life followed by an increase over time and this trend convinced us to perform urine analysis in the successive enrolled patients. We observed a positive correlation between mcBTT at 3rd week and the mean BE during the first week of life (r ¼ 0.22; p ¼ 0.00) (Table 2) and a negative correlation between mean BE during the first week of life and UCa/UCr on day 21 (r ¼ 0.35; p ¼ 0.01) (data not shown). This suggested us a role of metabolic acidosis during the first week of life on bone status of our population that could explain mcBTT deflection. Acidosis increased renal calcium excretion in a group of preterm
Bold values show statistical significance with p-value50.05. Table 3. Correlation between mcBTT and anthropometric and clinical parameters. Basal mcBTT
Gestational age Birth weight Length at birth Weight, 21 days Weight, 36 wk of GA Length, 21 days Length, 36 wk of GA Day to reach 1800 g TPN period Mechanical ventilation period
mcBTT, 3rd wk of life
mcBTT at 36 wk of GA
Pearson’s correlation
Sig. (two tailed)
Pearson’s correlation
Sig. (two tailed)
Pearson’s correlation
Sig. (two tailed)
0.23 0.40 0.20 0.40 0.34 0.19 0.29 – – –
0.00 0.00 0.02 0.00 0.00 0.04 0.00 – – –
0.30 0.43 0.17 0.42 0.19 0.28 0.26 0.31 0.30 0.21
0.00 0.00 0.03 0.00 0.03 0.00 0.00 0.00 0.00 0.01
0.23 0.30 0.02 0.32 0.26 0.17 0.30 0.30 0.05 0.24
0.01 0.00 0.77 0.00 0.00 0.11 0.00 0.00 0.60 0.00
Bold values show statistical significance with p-value50.05.
1345
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
1346
M. Betto et al.
infants, causing physiochemical dissolution with net alkali release from bone [15]. We evaluated biochemical parameters that could be markers of bone status, and their relationship with ultrasound parameters; some studies had already investigated this topic but with conflicting results. Using DEXA in preterm newborns, Backstrom et al. showed that the combination of ALP 4900 IU/L and phosphate 51.8 mmol/L could be a screening test for low mineral density [16] but correlations between bone mineral content obtained by DEXA and ALP or serum phosphate were not confirmed in Faerk’s study [17]. Catache et al. compared biochemical parameters with radiological signs of mineral deficiency and suggested the role of urinary levels of calcium in the early detection of demineralization, even if X-ray is not the method of choice for the early diagnosis of MBD [18]. Some studies investigated these topics with QUS method and negative correlations between ALP and tibial SOS were detected [19,20]; mean tibial SOS Z-score of infants with ALP 900 IU/L was significantly lower than that of the infants with ALP5900 UI/ L in Altuncu’s study [21]. A recent study, confirmed an inverse correlation between QUS measurements and ALP in a population of preterm and term infants but there was no correlation of altered QUS measurements over time with calcium and phosphate concentrations in urine and serum [22]. However, in the same study there was a highly significant inverse correlation of ALP with phosphate concentration in urine suggesting that lower phosphaturia is a marker of worsening bone status. In our study, we observed a direct correlation between mcBTT at 3rd week and serum phosphate on day 21, but not with ALP on day 21, as in other studies [23]. ALP is used as a marker of bone metabolism, but this value is the sum of three isoforms (liver, intestine and bone); even if bone isoform contributes to a large proportion of serum ALP, role of the other isoforms have to be considered in infants with gastrointestinal or hepatic disease [24]. In fact, we enrolled preterm infants needing parenteral nutrition at high risk to develop intolerance to enteral nutrition and cholestasis; for these reasons total ALP could not have been correlated to mcBTT. In a subgroup of patients, mcBTT at 3rd week positively correlated with urinary excretion of phosphate (r ¼ 0.34; p ¼ 0.01) and negatively correlated with urinary excretion of calcium (r ¼ 0.28; p ¼ 0.03): decreasing of UPO4/UCr and increasing of UCa/UCr could be a sign of worsening bone metabolism. It is interesting to underline that urinary excretion of phosphate on day 21 also positively correlated with mcBTT at 36 weeks of GA (r ¼ 0.24; p ¼ 0.00). Aladangady et al. assessed urinary calcium and phosphate creatinine ratios in a population of premature infants between 24 and 34 GA: patients in parenteral nutrition had higher UCa/UCr and lower UPO4/UCr, showing decreased utilization of calcium for bone growth due to phosphate depletion and lower protein intake [12]. We observed a direct correlation between urinary excretion of phosphate and serum phosphate (r ¼ 0.40; p ¼ 0.01), so we could confirm that neonates with phosphate depletion have a lower phosphaturia and a worsened mcBTT. These results suggest the use of urinary parameters as screening test to assess bone status.
J Matern Fetal Neonatal Med, 2014; 27(13): 1343–1347
A limit of our results could be that the r values are small suggesting that a greater part of the variance is not explained even though the analyzed parameters are statistically significant. Nonetheless, we want to outline that the sensitivity of the mcBTT measurement is sufficiently high to reveal the influence of metabolic factors on the mcBTT variations, indicating that this parameter can identify particular changes in the bone tissue related to metabolic effects. The negative correlations between mcBTT at 3rd week and TPN period, mechanical ventilation period and days to reach 1800 g, reflect the influence of clinical status of ill neonates on bone metabolism. In particular, the use of TPN is associated with MBD and the etiology is likely multifactorial: inadequate supply of proteins and energy could compromise the synthesis of bone tissue [4]; the amount of calcium and phosphate supplied by TPN could be inadequate to match the in utero mineral accretion rates and it could depend on the solubility of the pharmacological preparations and to the restriction of fluids intake. Moreover, other clinical conditions related to TPN may influence bone status, e.g. gastrointestinal and liver diseases, effect of hormones and renal control, immobilization, therapy with drug-induced alteration in bone metabolism and lack of enteral nutrition [25]. Enteral nutrition is more physiological and preterm formulas actually in use and fortification of human milk have improved minerals and proteins intakes in premature infants. Ventilation period seems to play a key role in the development of MBD, possibly due to concomitant immobilization; mechanical factors and muscle activities play a part in improving bone growth [26,27], so, during inactivity the bones could get weaker [3] and this could explain the negative correlation between days of mechanical ventilation and mcBTT. In conclusion, in our study, serum phosphate correlates most with ultrasound parameters of bone status (mcBTT). Low urinary excretion of phosphate, high urinary excretion of calcium and low serum phosphate could be regarded as early markers of inadequate bone development. QUS may have a significant role in monitoring bone health in preterm infant. We know that bone health in the analyzed preterm babies is not completely explained by the variables investigated in the present study. Further studies, including a larger number of infants, and a long-term follow-up, could help us in better understanding which are the variables more linked to bone growth and the possible influence of early bone status in future bone health.
Declaration of interest The authors report no conflicts of interest and have nothing to disclose.
References 1. Ryan S. Nutritional aspects of metabolic bone disease in the newborn. Arch Dis Child 1996;74:F145–8. 2. Scattolin S, Gaio P, Betto M, et al. Parenteral amino acid intakes: possible influences of higher intakes on growth and bone status in preterm infants. J Perinatol 2013;33:33–9. 3. Rauch F, Schoenau E. Skeletal development in premature infants: a review of bone physiology beyond nutritional aspects. Arch Dis Child Fetal Neonatal Ed 2002;86:F82–5. 4. Rigo J, Senterre J. Nutritional needs of premature infants: current issues. J Pediatr 2006;149:s80–8.
J Matern Fetal Neonatal Med Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
DOI: 10.3109/14767058.2013.858317
5. Rigo J, Nyamugabo K, Picaud JC, et al. Reference values of body composition obtained by dual energy X-ray absorptiometry in preterm and term neonates. J Pediatr Gastroenterol Nutr 1998;27: 184–90. 6. Dabezies EJ, Warren PD. Fractures in very low birth weight infants with rickets. Clin Orthop Relat Res 1997;335:233–9. 7. Fewtrell MS, Cole TJ, Bishop NJ, Lucas A. Neonatal factors predicting childhood height in preterm infants: evidence for a persisting effect of early metabolic one disease? J Pediatr 2000;137: 668–73. 8. Visser F, Spij AJ, Brus F. The validity of biochemical markers in metabolic bone disease in preterm infants: a systematic review. Acta Paediatr 2012:101:562–8. 9. Koletzko B, Goulet O, Hunt J, et al. Guidelines on Paediatric Parenteral Nutrition of the European Society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) and the European Society for Clinical Nutrition and Metabolism (ESPEN), supported by the European Society of Paediatric Research (ESPR). J Pediatr Gastroenterol Nutr 2005;41:S1–87. 10. Ritschl E, Wehmeijer K, De Terlizzi F, et al. Assessment of skeletal development in preterm and term infants by Quantitative Ultrasound. Pediatr Res 2005;58:1–7. 11. Rubinacci A, Moro GE, Boehm G, et al. Quantitative ultrasound for the assessment of osteopenia in preterm infants. Eur J Endocrinol 2003;149:307–15. 12. Aladangady N, Coen PG, White MP, et al. Urinary excretion of calcium and phosphate in preterm infants. Pediatr Nephrol 2004;19: 1225–31. 13. DeTerlizzi F, Battista S, Cavani F, et al. Influence of bone tissue density and elasticity on ultrasound propagation: an in vitro study. J Bone Mineral Res 2000;15:2458–66. 14. Bajaj M, Koo W, Hammami M, Hockman EM. Effect of subcutaneous fat on quantitative bone ultrasound in chicken and neonates. Pediatr Res 2010;68:81–3. 15. Kalhoff H, Diekmann L, Rudloff S, Manz F. Renal excretion of calcium and phosphorus in premature infants with incipient late metabolic acidosis. J Pediatr Gastroenter Nutr 2001;33:565–9.
Quantitative ultrasound in preterm infants
1347
16. Backstrom MC, Kouri T, Kuusela AL, et al. Bone isoenzyme of serum alkaline phosphatase and serum inorganic phosphate in metabolic bone disease of prematurity. Acta Paediatr 2000;89: 867–73. 17. Faerk J, Peitersen B, Petersen S, Michaelsen KF. Bone mineralisation in premature infants cannot e predicted from serum alkaline phosphatase or serum phosphate. Arch Dis Child Fetal Neonatal Ed 2002;87:F133–6. 18. Catache M, Leone CR. Role of plasma and urinary calcium and phosphorus measurements in early detection of phosphorus deficiency in very low birthweight infants. Acta Paediatr 2003;92: 76–80. 19. Tomlinson C, McDevitt H, Ahmed SF, White MP. Longitudinal changes in bone health as assessed by the speed of sound in very low birth weight infants. J Pediatr 2006;148:450–5. 20. Nemet D, Dolfin T, Wolach B, Eliakim A. Quantitative ultrasound measurements of bone speed of sound in premature infants. Eur J Pediatr 2001;160:736–40. 21. Altuncu E, Akman I, Yurdakul Z, et al. Quantitative ultrasound and biochemical parameters for the assessment of osteopenia in preterm infants. J Matern Fetal Neonatal Med 2007;20:401–5. 22. Rack B, Lochmu¨ller E-M, Janni W, et al. Ultrasound for the assessment of bone quality in preterm and term infants. J Perinatol 2012;32:218–26. 23. Fewtrell MS, Loh KL, Chomtho S, et al. Quantitative ultrasound (QUS): a useful tool for monitoring bone health in preterm infants? Acta Paediatr 2008;97:1625–30. 24. McDevitt H, Ahmed SF. Quantitative ultrasound assessment of bone health in the neonate. Neonatology 2007;91:2–11. 25. Klein GL. Metabolic bone disease of total parenteral nutrition. Nutrition 1998;14:149–52. 26. Moyer-Mileur LJ, Ball SD, Brunstetter VL, Chan GM. Maternaladministered physical activity enhances bone mineral acquisition in premature very low birth weight infants. J Perinatol 2008;28:432–7. 27. Vignochi CM, Silveira RC, Miura E, et al. Physical therapy reduces bone resorption and increased bone formation in preterm infants. Am J Perinatol 2012;29:573–8.
