Clin Exp Nephrol DOI 10.1007/s10157-014-1042-6
ORIGINAL ARTICLE
Reference glomerular filtration rate levels in Japanese children: using the creatinine and cystatin C based estimated glomerular filtration rate Osamu Uemura • Takuhito Nagai • Kenji Ishikura • Shuichi Ito Hiroshi Hataya • Yoshimitsu Gotoh • Naoya Fujita • Yuko Akioka • Tetsuji Kaneko • Masataka Honda
•
Received: 11 August 2014 / Accepted: 5 October 2014 Ó Japanese Society of Nephrology 2014
Abstract Background The present study was performed to determine the reference values of glomerular filtration rate (GFR) in children by age using the new eGFR equations derived from serum creatinine (Cr) and cystatine C (cysC). Methods A total of 1137 children (509 males and 628 females) between the ages of 3 months and 16 years presenting at our facilities between 2008 and 2009 without diseases affecting the renal function were included in this study as in our previous reports for reference values of serum Cr and cysC. We calculated eGFR with the Cr based equation in children aged 2–16 years, and with the cysC based equation in those aged 3–23 months, and determined the reference values of GFR in Japanese children by each age group. Results We reviewed the median, 2.5 and 97.5 percentile of GFR reference value in each age group. The medians of reference GFRs are 91.7, 98.5, 106.3, and 113.1 mL/min/1.73 m2 in children aged 3–5, 6–11, 12–17, and 18 months–16 years, respectively. Conclusion We determined the normal reference values of GFR in children. It is important for pediatricians who examine pediatric chronic kidney disease patients to know the values of normal renal function. Keywords Children Creatinine Cystatin C Glomerular filtration rate Reference levels O. Uemura T. Nagai K. Ishikura S. Ito H. Hataya Y. Gotoh N. Fujita Y. Akioka T. Kaneko M. Honda The Committee of Measures for Pediatric CKD, The Japanese Society for Pediatric Nephrology, Tokyo, Japan O. Uemura (&) Department of Pediatric Nephrology, Aichi Children’s Health and Medical Center, 1-2 Osakada Morioka-cho, Obu, Aichi 474-8710, Japan e-mail: [email protected]
Introduction Renal inulin clearance (Cin) to measure glomerular filtration rate (GFR) directly is compromised by problems of collecting urine samples in children. Therefore, Schwartz et al. expressed the serum creatinine (Cr) based estimated GFR (eGFR; ml/min/1.73 m2) by k 9 body length (cm)/ serum Cr level (mg/dL) by the Jaffe method Cr determination in 1987 [1], and by enzymatic Cr determination in children 1–16 years old in 2009 [2]. We doubt whether the new Schwartz equations can be used to estimate the GFR in Japanese children with chronic kidney disease (CKD), because there are differences in renal function and muscle mass between Japanese and American individuals and only one common ‘‘bedside’’ linear equation is used in children aged from 1 to 16 years, including the period of adolescence [3]. Therefore, we determined the reference values of serum creatine (Cr) and cystatin C (cysC) [4, 5] and derived formulas to estimate glomerular filtration rate based on enzymatic Cr and cysC determination in Japanese children [6, 7]. However, we have no reference value of GFR in Japanese children, and there are few reports on detailed reference values of GFR in children by age. The present study was performed to determine the reference values of GFR in children by age group using the new eGFR equations derived from serum Cr and cysC.
Materials and methods Study population A total of 1137 children (509 males and 628 females) between the ages of 3 months and 16 years presenting at
123
Clin Exp Nephrol
the facilities of the members for the Committee of Measures for Pediatric Chronic Kidney Disease and Tokyo Health Service Association between 2008 and 2009 without kidney disease, urogenital disease, infectious disease, inflammatory disease, dehydration, muscular disease, anomaly syndrome, malignant disease, hypertension, cardiovascular disease, liver or pancreas disease, or pregnancy were included in this study as in past reports of reference values of serum Cr [4] and cysC [5]. Of the total study population shown in Table 1, 45 % were male, and 58 % were enrolled on preoperative examination. The median age was 6.9 years, median height was 117.5 cm, and median weight was 21.7 kg. The median values of serum Cr and cysC were 0.36 mg/dL and 0.78 mg/L, respectively. The study was approved by the local ethics boards, and written informed consent was obtained from the parents of each subject. The ethics committee approval number in Aichi Children’s Health and Medical Center is 200706. Serum Cr and cysC measurements, and Cr-based and cysC-based eGFR calculations The serum Cr level was determined by an enzymatic method as reported previously [4]. The serum cysC level Table 1 Characteristics of 1137 children included in this study Characteristics
Median (IQR)a
Total Age (year)
n 1137
6.9 (3.9–12.2)
\2 years
132
C2 years
1005
was determined using the cysC assay: Nescaute GC cystatin C (Alfresa Pharma Corporation) as reported previously [5]. In Japan, the standardized method of cystatin C measurement traceable to ERM-DA471/IFCC became available in 2011. In the present study, serum cysC values of 174 samples were measured by the colloidal gold immunoassay before 2011 and were calibrated to a standardized value using the correction factor 0.96 which showed calculated cysC reflected the standardized cysC actually measured [7]. The pediatric Cr based equation [6] was calculated as shown below; eGFR (mL/min/1.73 m2) = 110.2 9 (reference serum Cr (mg/dL)/patient’s serum Cr (mg/dL)) ? 2.93. Reference serum Cr levels (y) are shown by the following two equations of body length (x): Males: y = -1.259x5 ? 7.815x4 - 18.57x3 ? 21.39x2 - 11.71x ? 2.628 Females: y = -4.536x5 ? 27.16x4 - 63.47x3 ? 72.43 2 x - 40.06x ? 8.778 The pediatric cysC based equation [7] was calculated as shown below; eGFR (mL/min/1.73 m2) = 104.1/serum cysC (mg/L) - 7.80 Cr based eGFR is not suitable for children aged under 2 years. The Flanders metadata equation based by Cr and age developed by Pottel et al. [8] is proposed for children between 1 month and 14 years of age. However, the valuables of our formulas do not include age. Therefore, we calculated eGFR with a Cr based equation in children aged 2–16 years, and with a cysC based equation in those aged 3–23 months.
Gender Male
509
Female 117.5 (99.1–150.0)
Weight (kg)
21.7 (15.0–41.2)
Serum creatinine (mg/dL)
0.36 (0.28–0.48)
Serum cystatin C (mg/L) Reasons for blood tests Preoperative evaluation
Results
0.78 (0.72–0.84) 655
Strabismus
292
Inguinal hernia
270
Blepharoptosis
42
Congenital hip dislocation
10
Cataract
9
Entropion of lids
8
Others Health examination
a
628
Height (cm)
24 356
Allergen examination
38
Miscellaneous
88
IQR interquartile range
123
We examined the correlations between eGFR and age in all subjects by gender (Fig. 1). Scattergrams showed that reference eGFR slightly increases with age only in infants. We reviewed the median, 2.5 and 97.5 percentile of GFR reference value in each age group, regardless of gender between age 3 and 23 months, and by gender between 2 and 16 years (Table 2). We determined a reference value of eGFR for males and females aged between 18 months and 16 years (Table 3), because in these age and gender groups the distributions of the reference values seemed to differ only slightly and we thought that accuracy increased with increased number of cases. The medians of reference GFRs are 91.7, 98.5, 106.3, and 113.1 mL/min/1.73 m2 in children aged 3–5, 6–11, 12–17, and 18 months–16 years, respectively. In addition, it is simple and easy to use at the bedside.
Clin Exp Nephrol males
250
females
250
200
eGFR (ml/min/1.73m2)
eGFR (ml/min/1.73m2)
Fig. 1 Correlations between eGFR and age in subjects by gender. Scattergrams showing reference eGFR slightly increase with age only in infants
150
100
50
0
200
150
100
50
0 0
5
10
Age (years)
Discussion Cin is the gold standard for evaluations of kidney functions, but cannot be measured easily. Therefore, the Schwartz formulas by the Jaffe method Cr determination [1] have been widely used to estimate GFR in children worldwide. Recently, however, enzymatic methods have been used to measure Cr rather than the Jaffe method, and the original Schwartz equations are not accurate using creatinine measured enzymatically. Schwartz et al. reported the updated formula, the so-called ‘‘bedside’’ version, as eGFR = 0.413 9 body length (cm)/serum Cr level (mg/ dL) by the enzymatic method showing a 25 % reduction in value of k from the previous value of 0.55 generated from Jaffe-based serum Cr measurements [2]. They concluded that the formula can be used in American children aged 1–16 years. We have reported that the new Schwartz bedside formula cannot be used to estimate GFR in Japanese children with normal renal function between 1 and 16 years, including the adolescent period [3]. There seems to be a large problem in that the ranges of the reference value for boys [12 years old and girls [14 years old overlap with the range for CKD stage 2. We doubted whether the new ‘‘bedside’’ Schwartz formula could be used to estimate GFR in Japanese pediatric CKD patients as well as in children with normal renal function. Therefore, we have established two estimated creatinine-based GFR equations for use in Japanese children aged between 2 and 11 years [9] and in Japanese children and adolescents aged between 2 and 18 years [6]. In addition, we have derived a cystatin C based estimated GFR equations in Japanese children and adolescents aged between 1 month and 18 years, including infants [7]. In the present study, we presented the reference GFR levels in Japanese children using the Cr and cysC based eGFR, in children aged 2–16 years and aged 3–23 months, respectively.
15
20
0
5
10
15
20
Age (years)
The rise in GFR from birth to adulthood is well known. In brief, GFR rises to around 100 mL/min/1.73 m2 by about 1 year, and mature values of GFR range from 100 to 120 mL/min/1.73 m2 [10]. However, a few reports give detailed reference values of GFR in children by age. The present study was performed to determine the reference values of GFR in children by each group using the new eGFR equations derived from serum Cr [6] and cysC [7], and reference values of serum Cr [4] and cysC [5] in Japanese children aged between 3 months and 16 years. The medians of reference GFRs were 91.7, 98.5, 106.3, and 113.1 mL/min/1.73 m2 in 3–5, 6–11, 12–17, and 18 months–16 years old, respectively, and showed a gradual increase with age, but were approximately constant between 18 months and 16 years old. Brodehl et al. reported that GFRs derived from Cin approached adult levels within 2 years and were approximately constant between 3 and 15 years, showing values of 111.2 and 117.2 mL/min/1.73 m2 at 3–4 years and 13–15 years, respectively [11]. Piepsz et al. reported that there was a progressive increase in chromium-51 ethylene diamine tetra-acetic acid clearance from the first weeks of life with a plateau at around 18 months, and between 2 and 17 years of age, the clearance values remained constant, with a mean value of 114 ml/min/1.73 m2 (SD: 24 ml/min) [12]. Despite the racial difference, our report and theirs considerably agree. The present study has some limitations. First, we calculated eGFR with Cr based equation in children aged 2–16 years, and with cysC based equation aged 3–23 months, respectively. This is because Cr based eGFR is not suitable for children under 2 years of age. Second, in this study we did not undergo Cin, but utilized eGFR equations derived from serum Cr or cysC in children without diseases affecting renal function. Therefore, we should call these the reference value of eGFR rather than GFR. Third, we have not validated our equations, including
123
Clin Exp Nephrol Table 2 The median, 2.5 and 97.5 percentile of GFR reference value in each age group, regardless of gender between 3 and 23 months, and by gender between 2 and 16 years
Table 3 The median, 2.5 percentile, and 97.5 percentile of GFR reference value in each age group regardless of gender between 3 months and 16 years old
Age
Gender
n
2.5 % tile
50 % tile
Age 3–5 months
17
76.6
91.7
106.7
3–5 months
Male and female
17
76.6
91.7
106.7
6–11 months
47
75.7
98.5
133.0
6–11 months
Male and female
47
75.7
98.5
133.0
12–17 months 18 months–16 years
31 1042
83.3 83.5
106.3 113.1
132.6 156.7
12–17 months
Male and female
31
83.3
106.3
132.6
18–23 months
Male and female
37
97.9
115.4
138.7
2 years 3 years 4 years 5 years
97.5 % tile
Male
41
79.5
115.3
151.2
Female
34
102.3
118.7
166.0
Male
48
81.0
119.2
174.0
Female
41
89.8
116.8
154.0
Male
43
95.1
120.0
164.5
Female
37
87.6
111.9
159.3
Male
47
81.5
109.8
142.6
Female
48
90.9
109.6
133.5
6 years
Male Female
44 57
83.9 87.9
109.8 116.5
146.6 153.6
7 years
Male
37
85.2
108.0
153.4
Female
47
81.8
113.6
145.9
Male
18
82.5
103.7
135.7
Female
38
88.8
109.7
152.8
8 years 9 years 10 years 11 years 12 years
Male
18
89.1
109.9
137.7
Female
17
95.3
108.0
139.4
Male
11
94.0
113.4
155.2
Female
32
86.8
113.1
178.9
Male
19
94.5
122.9
147.7
Female
39
99.7
123.1
153.8
Male
15
95.1
117.5
161.6
Female
54
92.2
110.4
149.9
13 years
Male
30
89.2
115.8
164.7
14 years
Female Male
38 17
90.2 78.2
115.6 108.1
137.8 149.4
Female
40
88.2
106.6
134.5
Male
15
77.5
116.1
146.5
Female
22
80.6
112.2
134.0
Male
30
81.0
106.5
132.8
Female
28
82.7
108.4
130.7
15 years 16 years
in general children. The equation may lose its accuracy at different GFR levels [13]. However, we had determined s-Cr and cysC based eGFR equations in cases with GFR \ 150 mL/min/1.73 m2 [6, 7]; therefore, our equations may be reliable in general population same as in CKD patients.
123
n
2.5 % tile
50 % tile
97.5 % tile
However, we consider that these reference GFR values are sufficient to evaluate the quality of renal function in children. It is important for pediatricians who examine pediatric CKD patients to know the normal renal function. Acknowledgments Financial support from the Kidney Foundation, Japan, enabled us to examine blood and urine specimens collected throughout Japan. We thank Takeshi Matsuyama, MD, Yohei Ikezumi, MD, Midori Awazu, MD, Takashi Sekine, MD, Takuji Yamada, MD, Yuko Akioka, MD, Hirotsugu Kitayama, MD, Mayumi Sako, MD, Masataka Hisano, MD and Kazumoto Iijima, MD, of the Committee of Measures for Pediatric CKD, for their contributions to the improvement of this manuscript. Conflict of interest interest exists.
The authors have declared that no conflict of
References 1. Schwartz GJ, Brion LP, Spitzer A. The use of plasma creatinine concentration for estimating glomerular filtration rate in infants, children, and adolescents. Pediatr Clin North Am. 1987;34: 571–90. 2. Schwartz GJ, Mun˜oz A, Schneider MF, Mak RH, Kaskel F, Warady BA, Furth SL. New equations to estimate GFR in children with CKD. J Am Soc Nephrol. 2009;20:629–37. 3. Uemura O, Honda M, Matsuyama T, Ishikura K, Hataya H, Nagai T, Ikezumi Y, Fujita N, Ito S, Iijima K. Japanese Society for Pediatric Nephrology, the Committee of Measures for Pediatric CKD. Is the new Schwartz equation derived from serum creatinine and body length usable for evaluation of renal function in Japanese children? Eur J Pediatr. 2012;171:1401–4. 4. Uemura O, Honda M, Matsuyama T, Ishikura K, Hataya H, Yata N, Nagai T, Ikezumi Y, Fujita N, Ito S, Iijima K, Kitagawa T. Age, gender, and body length effects on reference serum creatinine levels determined by an enzymatic method in Japanese children: a multicenter study. Clin Exp Nephrol. 2011;15:694–9. 5. Yata N, Uemura O, Honda M, Matsuyama T, Ishikura K, Hataya H, Nagai T, Ikezumi Y, Fujita N, Ito S, Iijima K, Saito M, Keneko T, Kitagawa T. Reference ranges for serum cystatin C measurements in Japanese children by using 4 automated assays. Clin Exp Nephrol. 2013;17:872–6. 6. Uemura O, Nagai T, Ishikura K, Ito S, Hataya H, Gotoh Y, Fujita N, Akioka Y, Kaneko T, Honda M. Creatinine-based equation to estimate the glomerular filtration rate in Japanese children and adolescents with chronic kidney disease. Clin Exp Nephrol. 2013;. doi:10.1007/s10157-013-0856-y. 7. Uemura O, Nagai T, Ishikura K, Ito S, Hataya H, Gotoh Y, Fujita N, Akioka Y, Kaneko T, Honda M. Cystatin C-based equation to estimate glomerular filtration rate in Japanese children and
Clin Exp Nephrol adolescents. Clin Exp Nephrol. 2013;. doi:10.1007/s10157-0130910-9. 8. Pottel H, Mottaghy FM, Zaman Z, Martens F. On the relationship between glomerular filtration rate and serum creatinine in children. Pediatr Nephrol. 2010;25:927–34. 9. Nagai T, Uemura O, Ishikura K, Ito S, Hataya H, Gotoh Y, Fujita N, Akioka Y, Kaneko T, Honda M. Creatinine-based equations to estimate glomerular filtration rate in Japanese children aged between 2 and 11 years old with chronic kidney disease. Clin Exp Nephrol. 2013;17:877–81. 10. Friedman A. Laboratory assessment and investigation of renal function. In: Avner ED, Harmon WE, Niaudet P, Yoshikawa N,
editors. Pediatric Nephrology. 6th ed. Heiderberg: Springer; 2009. p. 491–504. 11. Brodehl J, Gellissen K, Weber HP. Postnatal development of tubular phosphate reabsorption. Clin Nephrol. 1982;17:163–71. 12. Piepsz A, Pintelon H, Ham HR. Estimation of normal chromium51 ethylene diamine tetra-acetic acid clearance in children. Eur J Nucl Med. 1994;21:12–6. 13. Sharma AP, Yasin A, Garg AX, Filler G. Diagnostic accuracy of cystatin C-based eGFR equations at different GFR levels in children. Clin J Am Soc Nephrol. 2011;6:1599–608.
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ORIGINAL ARTICLE
Reference glomerular filtration rate levels in Japanese children: using the creatinine and cystatin C based estimated glomerular filtration rate Osamu Uemura • Takuhito Nagai • Kenji Ishikura • Shuichi Ito Hiroshi Hataya • Yoshimitsu Gotoh • Naoya Fujita • Yuko Akioka • Tetsuji Kaneko • Masataka Honda
•
Received: 11 August 2014 / Accepted: 5 October 2014 Ó Japanese Society of Nephrology 2014
Abstract Background The present study was performed to determine the reference values of glomerular filtration rate (GFR) in children by age using the new eGFR equations derived from serum creatinine (Cr) and cystatine C (cysC). Methods A total of 1137 children (509 males and 628 females) between the ages of 3 months and 16 years presenting at our facilities between 2008 and 2009 without diseases affecting the renal function were included in this study as in our previous reports for reference values of serum Cr and cysC. We calculated eGFR with the Cr based equation in children aged 2–16 years, and with the cysC based equation in those aged 3–23 months, and determined the reference values of GFR in Japanese children by each age group. Results We reviewed the median, 2.5 and 97.5 percentile of GFR reference value in each age group. The medians of reference GFRs are 91.7, 98.5, 106.3, and 113.1 mL/min/1.73 m2 in children aged 3–5, 6–11, 12–17, and 18 months–16 years, respectively. Conclusion We determined the normal reference values of GFR in children. It is important for pediatricians who examine pediatric chronic kidney disease patients to know the values of normal renal function. Keywords Children Creatinine Cystatin C Glomerular filtration rate Reference levels O. Uemura T. Nagai K. Ishikura S. Ito H. Hataya Y. Gotoh N. Fujita Y. Akioka T. Kaneko M. Honda The Committee of Measures for Pediatric CKD, The Japanese Society for Pediatric Nephrology, Tokyo, Japan O. Uemura (&) Department of Pediatric Nephrology, Aichi Children’s Health and Medical Center, 1-2 Osakada Morioka-cho, Obu, Aichi 474-8710, Japan e-mail: [email protected]
Introduction Renal inulin clearance (Cin) to measure glomerular filtration rate (GFR) directly is compromised by problems of collecting urine samples in children. Therefore, Schwartz et al. expressed the serum creatinine (Cr) based estimated GFR (eGFR; ml/min/1.73 m2) by k 9 body length (cm)/ serum Cr level (mg/dL) by the Jaffe method Cr determination in 1987 [1], and by enzymatic Cr determination in children 1–16 years old in 2009 [2]. We doubt whether the new Schwartz equations can be used to estimate the GFR in Japanese children with chronic kidney disease (CKD), because there are differences in renal function and muscle mass between Japanese and American individuals and only one common ‘‘bedside’’ linear equation is used in children aged from 1 to 16 years, including the period of adolescence [3]. Therefore, we determined the reference values of serum creatine (Cr) and cystatin C (cysC) [4, 5] and derived formulas to estimate glomerular filtration rate based on enzymatic Cr and cysC determination in Japanese children [6, 7]. However, we have no reference value of GFR in Japanese children, and there are few reports on detailed reference values of GFR in children by age. The present study was performed to determine the reference values of GFR in children by age group using the new eGFR equations derived from serum Cr and cysC.
Materials and methods Study population A total of 1137 children (509 males and 628 females) between the ages of 3 months and 16 years presenting at
123
Clin Exp Nephrol
the facilities of the members for the Committee of Measures for Pediatric Chronic Kidney Disease and Tokyo Health Service Association between 2008 and 2009 without kidney disease, urogenital disease, infectious disease, inflammatory disease, dehydration, muscular disease, anomaly syndrome, malignant disease, hypertension, cardiovascular disease, liver or pancreas disease, or pregnancy were included in this study as in past reports of reference values of serum Cr [4] and cysC [5]. Of the total study population shown in Table 1, 45 % were male, and 58 % were enrolled on preoperative examination. The median age was 6.9 years, median height was 117.5 cm, and median weight was 21.7 kg. The median values of serum Cr and cysC were 0.36 mg/dL and 0.78 mg/L, respectively. The study was approved by the local ethics boards, and written informed consent was obtained from the parents of each subject. The ethics committee approval number in Aichi Children’s Health and Medical Center is 200706. Serum Cr and cysC measurements, and Cr-based and cysC-based eGFR calculations The serum Cr level was determined by an enzymatic method as reported previously [4]. The serum cysC level Table 1 Characteristics of 1137 children included in this study Characteristics
Median (IQR)a
Total Age (year)
n 1137
6.9 (3.9–12.2)
\2 years
132
C2 years
1005
was determined using the cysC assay: Nescaute GC cystatin C (Alfresa Pharma Corporation) as reported previously [5]. In Japan, the standardized method of cystatin C measurement traceable to ERM-DA471/IFCC became available in 2011. In the present study, serum cysC values of 174 samples were measured by the colloidal gold immunoassay before 2011 and were calibrated to a standardized value using the correction factor 0.96 which showed calculated cysC reflected the standardized cysC actually measured [7]. The pediatric Cr based equation [6] was calculated as shown below; eGFR (mL/min/1.73 m2) = 110.2 9 (reference serum Cr (mg/dL)/patient’s serum Cr (mg/dL)) ? 2.93. Reference serum Cr levels (y) are shown by the following two equations of body length (x): Males: y = -1.259x5 ? 7.815x4 - 18.57x3 ? 21.39x2 - 11.71x ? 2.628 Females: y = -4.536x5 ? 27.16x4 - 63.47x3 ? 72.43 2 x - 40.06x ? 8.778 The pediatric cysC based equation [7] was calculated as shown below; eGFR (mL/min/1.73 m2) = 104.1/serum cysC (mg/L) - 7.80 Cr based eGFR is not suitable for children aged under 2 years. The Flanders metadata equation based by Cr and age developed by Pottel et al. [8] is proposed for children between 1 month and 14 years of age. However, the valuables of our formulas do not include age. Therefore, we calculated eGFR with a Cr based equation in children aged 2–16 years, and with a cysC based equation in those aged 3–23 months.
Gender Male
509
Female 117.5 (99.1–150.0)
Weight (kg)
21.7 (15.0–41.2)
Serum creatinine (mg/dL)
0.36 (0.28–0.48)
Serum cystatin C (mg/L) Reasons for blood tests Preoperative evaluation
Results
0.78 (0.72–0.84) 655
Strabismus
292
Inguinal hernia
270
Blepharoptosis
42
Congenital hip dislocation
10
Cataract
9
Entropion of lids
8
Others Health examination
a
628
Height (cm)
24 356
Allergen examination
38
Miscellaneous
88
IQR interquartile range
123
We examined the correlations between eGFR and age in all subjects by gender (Fig. 1). Scattergrams showed that reference eGFR slightly increases with age only in infants. We reviewed the median, 2.5 and 97.5 percentile of GFR reference value in each age group, regardless of gender between age 3 and 23 months, and by gender between 2 and 16 years (Table 2). We determined a reference value of eGFR for males and females aged between 18 months and 16 years (Table 3), because in these age and gender groups the distributions of the reference values seemed to differ only slightly and we thought that accuracy increased with increased number of cases. The medians of reference GFRs are 91.7, 98.5, 106.3, and 113.1 mL/min/1.73 m2 in children aged 3–5, 6–11, 12–17, and 18 months–16 years, respectively. In addition, it is simple and easy to use at the bedside.
Clin Exp Nephrol males
250
females
250
200
eGFR (ml/min/1.73m2)
eGFR (ml/min/1.73m2)
Fig. 1 Correlations between eGFR and age in subjects by gender. Scattergrams showing reference eGFR slightly increase with age only in infants
150
100
50
0
200
150
100
50
0 0
5
10
Age (years)
Discussion Cin is the gold standard for evaluations of kidney functions, but cannot be measured easily. Therefore, the Schwartz formulas by the Jaffe method Cr determination [1] have been widely used to estimate GFR in children worldwide. Recently, however, enzymatic methods have been used to measure Cr rather than the Jaffe method, and the original Schwartz equations are not accurate using creatinine measured enzymatically. Schwartz et al. reported the updated formula, the so-called ‘‘bedside’’ version, as eGFR = 0.413 9 body length (cm)/serum Cr level (mg/ dL) by the enzymatic method showing a 25 % reduction in value of k from the previous value of 0.55 generated from Jaffe-based serum Cr measurements [2]. They concluded that the formula can be used in American children aged 1–16 years. We have reported that the new Schwartz bedside formula cannot be used to estimate GFR in Japanese children with normal renal function between 1 and 16 years, including the adolescent period [3]. There seems to be a large problem in that the ranges of the reference value for boys [12 years old and girls [14 years old overlap with the range for CKD stage 2. We doubted whether the new ‘‘bedside’’ Schwartz formula could be used to estimate GFR in Japanese pediatric CKD patients as well as in children with normal renal function. Therefore, we have established two estimated creatinine-based GFR equations for use in Japanese children aged between 2 and 11 years [9] and in Japanese children and adolescents aged between 2 and 18 years [6]. In addition, we have derived a cystatin C based estimated GFR equations in Japanese children and adolescents aged between 1 month and 18 years, including infants [7]. In the present study, we presented the reference GFR levels in Japanese children using the Cr and cysC based eGFR, in children aged 2–16 years and aged 3–23 months, respectively.
15
20
0
5
10
15
20
Age (years)
The rise in GFR from birth to adulthood is well known. In brief, GFR rises to around 100 mL/min/1.73 m2 by about 1 year, and mature values of GFR range from 100 to 120 mL/min/1.73 m2 [10]. However, a few reports give detailed reference values of GFR in children by age. The present study was performed to determine the reference values of GFR in children by each group using the new eGFR equations derived from serum Cr [6] and cysC [7], and reference values of serum Cr [4] and cysC [5] in Japanese children aged between 3 months and 16 years. The medians of reference GFRs were 91.7, 98.5, 106.3, and 113.1 mL/min/1.73 m2 in 3–5, 6–11, 12–17, and 18 months–16 years old, respectively, and showed a gradual increase with age, but were approximately constant between 18 months and 16 years old. Brodehl et al. reported that GFRs derived from Cin approached adult levels within 2 years and were approximately constant between 3 and 15 years, showing values of 111.2 and 117.2 mL/min/1.73 m2 at 3–4 years and 13–15 years, respectively [11]. Piepsz et al. reported that there was a progressive increase in chromium-51 ethylene diamine tetra-acetic acid clearance from the first weeks of life with a plateau at around 18 months, and between 2 and 17 years of age, the clearance values remained constant, with a mean value of 114 ml/min/1.73 m2 (SD: 24 ml/min) [12]. Despite the racial difference, our report and theirs considerably agree. The present study has some limitations. First, we calculated eGFR with Cr based equation in children aged 2–16 years, and with cysC based equation aged 3–23 months, respectively. This is because Cr based eGFR is not suitable for children under 2 years of age. Second, in this study we did not undergo Cin, but utilized eGFR equations derived from serum Cr or cysC in children without diseases affecting renal function. Therefore, we should call these the reference value of eGFR rather than GFR. Third, we have not validated our equations, including
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Clin Exp Nephrol Table 2 The median, 2.5 and 97.5 percentile of GFR reference value in each age group, regardless of gender between 3 and 23 months, and by gender between 2 and 16 years
Table 3 The median, 2.5 percentile, and 97.5 percentile of GFR reference value in each age group regardless of gender between 3 months and 16 years old
Age
Gender
n
2.5 % tile
50 % tile
Age 3–5 months
17
76.6
91.7
106.7
3–5 months
Male and female
17
76.6
91.7
106.7
6–11 months
47
75.7
98.5
133.0
6–11 months
Male and female
47
75.7
98.5
133.0
12–17 months 18 months–16 years
31 1042
83.3 83.5
106.3 113.1
132.6 156.7
12–17 months
Male and female
31
83.3
106.3
132.6
18–23 months
Male and female
37
97.9
115.4
138.7
2 years 3 years 4 years 5 years
97.5 % tile
Male
41
79.5
115.3
151.2
Female
34
102.3
118.7
166.0
Male
48
81.0
119.2
174.0
Female
41
89.8
116.8
154.0
Male
43
95.1
120.0
164.5
Female
37
87.6
111.9
159.3
Male
47
81.5
109.8
142.6
Female
48
90.9
109.6
133.5
6 years
Male Female
44 57
83.9 87.9
109.8 116.5
146.6 153.6
7 years
Male
37
85.2
108.0
153.4
Female
47
81.8
113.6
145.9
Male
18
82.5
103.7
135.7
Female
38
88.8
109.7
152.8
8 years 9 years 10 years 11 years 12 years
Male
18
89.1
109.9
137.7
Female
17
95.3
108.0
139.4
Male
11
94.0
113.4
155.2
Female
32
86.8
113.1
178.9
Male
19
94.5
122.9
147.7
Female
39
99.7
123.1
153.8
Male
15
95.1
117.5
161.6
Female
54
92.2
110.4
149.9
13 years
Male
30
89.2
115.8
164.7
14 years
Female Male
38 17
90.2 78.2
115.6 108.1
137.8 149.4
Female
40
88.2
106.6
134.5
Male
15
77.5
116.1
146.5
Female
22
80.6
112.2
134.0
Male
30
81.0
106.5
132.8
Female
28
82.7
108.4
130.7
15 years 16 years
in general children. The equation may lose its accuracy at different GFR levels [13]. However, we had determined s-Cr and cysC based eGFR equations in cases with GFR \ 150 mL/min/1.73 m2 [6, 7]; therefore, our equations may be reliable in general population same as in CKD patients.
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n
2.5 % tile
50 % tile
97.5 % tile
However, we consider that these reference GFR values are sufficient to evaluate the quality of renal function in children. It is important for pediatricians who examine pediatric CKD patients to know the normal renal function. Acknowledgments Financial support from the Kidney Foundation, Japan, enabled us to examine blood and urine specimens collected throughout Japan. We thank Takeshi Matsuyama, MD, Yohei Ikezumi, MD, Midori Awazu, MD, Takashi Sekine, MD, Takuji Yamada, MD, Yuko Akioka, MD, Hirotsugu Kitayama, MD, Mayumi Sako, MD, Masataka Hisano, MD and Kazumoto Iijima, MD, of the Committee of Measures for Pediatric CKD, for their contributions to the improvement of this manuscript. Conflict of interest interest exists.
The authors have declared that no conflict of
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