The Journal of Arthroplasty 29 (2014) 2214–2218
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Whole blood metal ion measurement reproducibility between different laboratories Michel Rahmé, MD a, Martin Lavigne, MD, MSc b, Janie Barry, MSc b, Ciprian Mihai Cirtiu, PhD c, Patrick Bélanger, MSc c, Pascal-André Vendittoli, MD, MSc b, ⁎ a b c
Hôpital de Hautepierre, Strasbourg, France Hôpital Maisonneuve-Rosemont, Montréal, Québec, Canada Centre de toxicologie du Québec, Institut National de Santé Publique du Québec, Sainte-Foy, Québec, Canada
a r t i c l e
i n f o
Article history: Received 10 January 2014 Accepted 19 July 2014 Keywords: metal ion hip arthroplasty chromium cobalt
a b s t r a c t Monitoring patients' metal ion blood concentrations can be useful in cases of problematic metal on metal hip implants. Our objective was to evaluate the reproducibility of metal ion level values measured by two different laboratories. Whole blood samples were collected in 46 patients with metal on metal hip arthroplasty. For each patients, two whole blood samples were collected and analyzed by two laboratories. Laboratory 1 had higher results than laboratory 2. There was a clinically significant absolute difference between the two laboratories, above the predetermined threshold, 35% of Cr samples and 38% of Co samples. All laboratories do not use the same technologies for their measurements. Therefore, decision to revise a metal on metal hip arthroplasty should rely on metal ion trends and have to be done in the same laboratory. © 2014 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) has proven to be a highly effective treatment of hip osteoarthritis in the elderly which is the reason indications were subsequently extended to young and middle-aged adults as well. Increasing demands in these patient groups due to significant physical activity and higher life expectancy resulted in developing improved bearing materials. These bearings are characterized by potential combinations of highly cross-linked polyethylene, ceramic, or metal cup inserts with ceramic or metal heads. Metal-on-metal (MoM) bearings have been used with conventional THA for several decades with promising results from early applications [1–3]. Low wear potential of mechanically well investigated prostheses, no relevant risk of material fracture, excellent stability and a high design variability seemed to justify the application of MoM bearings in hip resurfacing (HR) and large head hip arthroplasty (LH-THA) [4–6]. Nevertheless, wear and corrosion of these implants may lead to a release of metal products including chromium (Cr) and cobalt (Co) into surrounding tissue and body fluids as well as internal organs. Metal accumulation may result in local “adverse reactions to metal debris” (ARMD) [7] and potentially induce systemic adverse effects (i.e. toxicity, teratogenicity and carcinogenicity) [8–11]. Although the toxicological significance of local and systemic elevations in metal ions has not been definitively established, monitoring patients with MoM bearings for elevated metal ion concentrations in the blood can The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.07.018. Reprint requests: Pascal-A Vendittoli MD, MSc, FRCS, Hôpital MaisonneuveRosemont, 5415 Boul L'Assomption, Montréal, Québec, H1T 2M4 Canada. http://dx.doi.org/10.1016/j.arth.2014.07.018 0883-5403/© 2014 Elsevier Inc. All rights reserved.
be useful in determining the performance of the bearing[12–14]. Metal ions from the corresponding alloying element (i.e. cobalt—Co, chromium —Cr, titanium—Ti, nickel—Ni, molybdenum—Mo) can be measured in the joint itself as well as in surrounding tissue and body fluids. Blood concentrations of ions released from well performing metal implants are low, often less than 1 μg/L [15]. Recent guidelines and metal ion level threshold values have been recently recommended to follow patients with metal and metal bearings THA [16]. As example, the UK Medicines and Healthcare products Regulatory Agency has issued a blood cobalt guidance value of 7 μg/L to identify MoM hip implant patients who may require closer surveillance due to an association with excessive implant wear. High-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) is one of the most sensitive and versatile techniques available for metal ions measurement and most clinicians are relying on results obtained with this analysis method [17,18]. The objective of this study was to evaluate whole blood metal ion levels drawn for the same patient at the same time, but analyzed in two different laboratories. The aim was to see if there was a difference between the laboratories that may be of clinical significance and that could lead to misinterpretation in the results. Material and Methods Study Population From July 2003 and October 2009, we collected whole blood samples in multiple patients with unilateral MoM hip arthroplasty.
M. Rahmé et al. / The Journal of Arthroplasty 29 (2014) 2214–2218
Many of these patients were taking part in structured research protocols with subsequent publications [12,13,19,20]. For the purpose of the present study, patients were eligible when at least two tubes of whole blood from the same collection time were available. Sample Collection For each patient, after discarding the first 5 cc of blood, three whole blood samples were collected in individual polypropylene syringes. For all procedures a twenty-two gauge stainless steel needle (BD Vialon Biomaterial IV catheter, 0.9 × 25 mm, 35 cc/min; Beckton Dickinson, Mississauga, Ontario) were used to cannulate the vein and the outer plastic cannula was left in place while the needle was discarded. All samples were transferred to individual polypropylene tubes (Lavander, K2 EDTA 7.2 mg for laboratory 1 and Royal blue, trace element K2 EDTA 10.8 mg for laboratory 2) and kept frozen at − 20 °C. Patients were asked to not modify their exercises routine or engage in new, strenuous activities, take new medications or undergo other venous sampling 1 week before blood collection. Samples were kept frozen at − 20 °C until analysis by the two different laboratories. Samples were analyzed from December 2011 to April 2013 for laboratory 1 and from March to June 2013 for laboratory 2. Laboratory 1 Analysis, ICP-MS The concentrations of Cr and Co ions in whole blood samples were measured with a single quadrupole ICP-MS Elan DRCII from PerkinElmer. The detection limits were 0.1 μg/L for Cr and 0.035 μg/L for Co. Blood samples were diluted in diluent containing 0.5% (v/v) NH4OH and 0.1% (v/v) octylphenol ethoxylate. External calibration curves were prepared by diluting human blood in diluent and spiking with different volumes of 1 mg L −1 multi-elements standard solution (SCP Science, PlasmaCal ICP-MS Verification Standard 1, 5% HNO3, #141-110-011) in order to emulate 0, 4, 20, 80, and 200 μg/L in the standards solutions. The internal standard for calibration standards and blood samples was yttrium 89 for Co59 (standard mode with correction equation) and indium 115 for Cr53 (DRC mode with ammonia as reaction gas). Commercial blood reference materials were used as controls to verify the results. Laboratory 2 Analysis, HR-ICP-MS The concentrations of Cr and Co ions in the whole blood samples were measured in an Element 2 High-Resolution, Sector-Field, Inductively Coupled Plasma Mass Spectrophotometer (Thermo Fisher Scientific GmBH, Bremen, Germany). The detection limits were 0.1 μg/L for Cr and 0.02 μg/L for Co. The blood samples were exposed to concentrated nitric acid to digest protein and concentrated hydrogen peroxide to digest lipids. After dilution with water and internal standard yttrium 89, the final sample was introduced into the instrument and compared against aqueous standards with commercial blood controls to verify the results. Statistical Significance The detection limit of the HR-ICP-MS is approximately 3 times the background noise of the samples. The limit of quantification, which determines more precisely the sensitivity and accuracy of the device, is approximately 10 times the background noise. The limit of quantification is therefore 3.33 times the limit of detection. For this study, we have used the very specific detection limit of the HR-ICP-MS used in laboratory 2 (0.1 μg/L and 0.02 μg/L for Cr and Co in whole blood) to establish the limit of quantification. Based on these values, we determined that a conservative difference of 3.5 times the detection limit will be considered statistically significant or 0.35 μg/L for Cr and 0.07 μg/L for Co.
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Clinical Significance We defined in a previous study that a variation in concentration above 1 μg/L for Cr and above 0.5 μg/L for Co could be clinically significant. These thresholds were established based on the average concentrations of Cr and Co varying between 0.5 and 3 μg/L in blood when implants are working well. In the event of a malfunction or clinical problem, the concentration of these ions usually increases dramatically from 2 to 20 μg/L. So, according to the authors, a variation in concentration of less than 1 μg/L for Cr and less than 0.5 μg/L for Co between results would not impact the clinical evaluation and patients follow up. Statistical Analysis Statistical analysis was performed using SPSS software, version 20.0. All patients with paired results were included in the study. Continuous values were presented as an average ± standard deviation with minimum and maximum values. Differences between pairs of sample were analyzed by a paired t-test with a confidence interval of 95%. Differences between pairs of samples (in absolute values) were analyzed by a simple t-test with a confidence interval of 95%. Proportion tests were performed with a chi-square test. Correlations between results of laboratories were analyzed with Pearson correlation. The difference between the reproducibility (mean difference) of the measure of chromium and cobalt metal ions was analyzed by Student's t-test for independent data. Statistical significance was set at 0.05. Ethical Considerations The research project was approved by the Scientific Committee and the Ethics Committee of our Centre. The study was explained to patients and informed consent was obtained. Results We have analyzed a total of 46 pairs of whole blood samples. Patient's mean age at the surgery was 50 years (range 28–65) and there were 24 men and 22 women. Thirty-six patients had large diameter femoral head THA, 9 patients a hip resurfacing (HR) and 1 patient a 28 mm THA. Fifty-one percent of hip implants were made by Zimmer, 18% by Biomet, 11% by Depuy and 20% by Smith Nephew. The mean follow-up at the blood collection time was 63 months (range 12–96). Samples were kept frozen for an average of 0.11 months (min 0, max 0.39 months) before analysis at laboratory 1 and 5.33 months (min 0.1, max 16.16) at laboratory 2. The distributions of Cr and Co concentrations from the two different laboratories are shown in Fig. 1 and Table 1. The concentrations obtained from laboratory 1 are significantly different than from laboratory 2. Table 2 and Fig. 2 show the distribution of differences between the two laboratories. Laboratory 1 had higher result than laboratory 2 with a CI (95%) of 0.30 to 1.23 for Cr and 0.12 to 0.93 for Co. The results of laboratory 1 were higher than those of laboratory 2 in 70 and 82% for Cr and Co respectively. The mean ratios between laboratory 1 and 2 are 1.30 (range 0.37 to 4.28) and 1.14 (range 0.46 to 2.12) for Cr and Co respectively. The distribution of absolute difference between the laboratories is shown in Table 3 and Fig. 3. The means absolute difference between the two laboratories was significant for Cr and Co metal ions measured. Thirty-five percent of paired samples for Cr and 38% for Co had an absolute difference above the predetermined threshold of clinical significance. We found a high statistical correlation between the laboratories for Cr (0.841) and Co (0.965) measured (P ≤ 0.001 for Cr and Co). The Bland and Altman graph, shown in Figs. 4 and 5, established that the
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M. Rahmé et al. / The Journal of Arthroplasty 29 (2014) 2214–2218 Table 2 Mean Differences (Laboratory 1–Laboratory 2) and Thresholds of Clinical Significance for Cr and Co.
Ion
n
Mean difference (μg/L) a
Standard deviation
Cr Co
46 45
0.76 [−2.62 to 7.32] 0.52 [3.15 to 4.99]
1.57 1.35
a
Fig. 1. Box plot of the concentration of Cr and Co metal ions in the two laboratories. Horizontal bars define the quartiles, with the second and third quartiles contained in the boxes. Circles represent outliers, defined as values that are 1.5 to 3 times higher than the values of the third quartile. The data identified with stars are extreme outliers, defined as values that are at least three times higher than the values of the third quartile.
agreement limits of Cr and Co measures are over the predetermined threshold of clinical significance. Furthermore, we did not find any significant difference between the reproducibility (mean difference) of the measure of Cr and Co metal ions (P = 0.441). Discussion
P-value 0.002 0.012
Threshold of clinical significance 1.0 0.5
Results are shown as the mean with minimum and maximum in square brackets.
measured by two different laboratories using similar analysis methods. Inter laboratory reproducibility for metal ion measurements in patients who underwent MoM THA is important as patients may travel from one surgeon to another or can be screened in different reference centers. The surgeon has to know if results coming from different laboratories can be reliable. Comparing 46 pairs of samples taken in the same patients and analyzed by two different laboratories, we found a statistical difference between the results (Table 1). The mean absolute difference was significant for Cr and Co metal ions measured and 35% of paired samples for Cr and 38% for Co had an absolute difference above the predetermined threshold of clinical significance (Table 3). The results of laboratory 1 were higher than those of laboratory 2 in 70 and 82% for Cr and Co respectively (Table 2). Regarding the ion analysis method, HR-ICP-MS has already been proven to be the gold standard method in metal ion analysis even though some laboratories still use atomic absorption spectrometry (AAS) [15,17,18]. In our study both laboratories were equipped with ICP-MS instruments, with the difference being that only laboratory 2 had a high resolution instrument. A high resolution device allows to discard some spectral interferences that are common with an ICP-MS analysis technology. Polyatomic interferences are known to occur in analysis by ICP-MS. However, when an analysis is directed to trace or ultratrace concentrations of metals, possible interferences that appeared to be insignificant or nonexistent can have an important impact on the validity of the analysis [26]. However not all subjects have interferences which could explain why the differences between the two laboratories are not systematic.
Metal-on-metal (MoM) bearings have been used with hip arthroplasty for several decades with promising results from early applications. Nevertheless, wear and corrosion of these implants lead to local and systemic metal products release. Monitoring patients' metal ion blood concentrations can be useful in determining the performance of the bearing and indicating need for revision surgery for problematic implants [21,22]. The level proposed as the indicator of well functioning small-diameter metal-on-metal THAs is 1 μg/L [23]. As some MoM implant may present higher than expected wear and metal ions release after implantation, clinical follow up and systemic metal ion release in patients' blood or serum were advised. Metal ion measurements allow the early detection of increased wear before extensive tissue destruction has occurred with a better outcome of revisions. Some authors and the National Institute recently proposed additional investigations and/or bearing revision when Cr and/or Co levels exceed 7 μg/L [24,25]. The objective of our study was to evaluate the reproducibility of metal ion levels values
Table 1 Distribution of the Concentrations of Cr and Co Metal Ions in Laboratories 1 and 2.
Ions Chromium Cobalt
Laboratory n 1 2 1 2
46 45
Minimum Maximum Average Standard P(μg/L) (μg/L) (μg/L) deviation value 0.45 0.46 0.35 0.29
13.01 6.71 17.68 13.55
3.04 2.27 4.51 3.98
2.65 1.59 4.50 3.67
0.002 0.012
Fig. 2. Box plot of the difference in concentration of Cr and Co metal ions for the two laboratories. Horizontal bars define the quartiles, with the second and third quartiles contained in the boxes. Circles represent outliers, defined as values that are 1.5 to 3 times higher than the values of the third quartile. The data identified with stars are extreme outliers, defined as values that are at least three times higher than the values of the third quartile.
M. Rahmé et al. / The Journal of Arthroplasty 29 (2014) 2214–2218
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Table 3 Mean Absolute Differences and Thresholds of Clinical Significance for Cr and Co in Two Different Laboratories.
Ion
n
Mean absolute difference (μg/L)
Cr Co
46 45
1.11 [0.01–7.32] 0.82 [0.01–4.99]
a
a
Standard deviation
P-value
Threshold of clinical significance
1.34 1.20
≤0.001 ≤0.001
1.0 0.5
Results are shown as the mean with minimum and maximum in square brackets.
Other variables can be taken into account for explaining the differences between the results of the two laboratories such as sample contamination, stability of the sample over time as well as the sampling protocol and the method itself. It is well known that Cr and Co are present as stabilizers and coloring agents in rubber products (stoppers, plunger seals) [27]. It has to be noticed that despite the fact that the samples were collected at the same time, the analyses were done at different times by the two laboratories, with gaps ranging from 1 to 18 months. Furthermore, the samples were collected in two different types of tubes. The first tube, containing 10.8 mg K2 EDTA (Royal blue trace elements) was sent to laboratory 2 while the second one, which had 7.2 mg K2 EDTA (Lavender) was sent to laboratory 1. This difference in the quantity of anticoagulant can be at the basis of matrix effects which could explain the disagreement between the results of the two laboratories. Moreover, the sample preparation prior to analysis is very different for both laboratories. Laboratory 1 proceeds through a simple dilution of the blood sample with a basic diluent combined with a matrix matched calibration while the procedure of laboratory 2 involves digestion of the samples and an aqueous calibration. This main difference could explain the differences observed between the laboratories. We also published recently the reproducibility of samples analyzed by the same laboratory [28]. The laboratory did blind analyses of 78 pairs of whole blood samples taken at the same time in the same patients. The absolute difference between the two samples was greater than the limit of quantification of the HR-ICP-MS device
Fig. 3. Box plot of the absolute difference in concentration of Cr and Co metal ions for the two laboratories. Horizontal bars define the quartiles, with the second and third quartiles contained in the boxes. Circles represent outliers, defined as values that are 1.5 to 3 times higher than the values of the third quartile. The data identified with stars are extreme outliers, defined as values that are at least three times higher than the values of the third quartile.
Fig. 4. Bland–Altman plot between chromium concentrations obtained in two different laboratories. The solid line indicates the mean difference (or bias); the dotted lines indicate the 95% limits of the agreement.
for all three ions (0.84 versus 0.35 mg/L for Cr, 0.74 versus 0.07 for Co, and 0.88 versus 0.70 mg/L for Ti). Although the levels were very small in most cases, they exceeded the clinical significant threshold in 19 to 31% of the cases. Given the results we had in this intra observer reproducibility study and the current one showing mismatch between two laboratories, as over 30% of the samples clinicians should be aware of such limited intra and inter laboratory reproducibility. Even though variations are not major, they are significant enough to risk misinterpretation in borderline cases for which revision surgery might be considered. This has to be taken into account when assessing a patient who had his previous metal ion measurements done in another laboratory. Results must whenever possible be compared to results from the same laboratory to avoid the risk of misinterpreting inter-laboratory variations. Moreover, it is important to base our clinical decision on a metal ion unfavorable trend over a certain period and not on a simple elevated measure. Absolute values taken out of context are less meaningful. This is why we recommend having the measurements done in the same laboratory, so that the values obtained are as accurate as possible.
Fig. 5. Bland–Altman plot between the cobalt concentrations obtained in two different laboratories. The solid line indicates the mean difference (or bias); the dotted lines indicate the 95% limits of the agreement.
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M. Rahmé et al. / The Journal of Arthroplasty 29 (2014) 2214–2218
Conclusion Ion metal blood screening is a common way of detecting malfunctioning MoM hip arthroplasty, in association with clinical and radiological findings. However, all laboratories do not use the same technologies or calibrations to do these measurements. Even though variations are not major, we found that they are significant enough in more than 1/3 of the cases to risk misinterpretation in borderline cases. Therefore, decision to revise a metal on metal hip arthroplasty should not rely on a simple metal ion measurement and should include patient symptoms and radiographic evidences of implant dysfunction. References 1. Dorr LD, Wan Z, Dubois B, et al. Total hip arthroplasty with use of the Metasul metal-on-metal articulation. Four to seven-year results. J Bone Joint Surg Am 2000; 82(6):789. 2. Wagner M, Wagner H. Medium-term results of a modern metal-on-metal system in total hip replacement. Clin Orthop Relat Res 2000;379:123. 3. Weber BG. Experience with the Metasul total hip bearing system. Clin Orthop Relat Res 1996(329 Suppl):S69. 4. Amstutz HC, Beaulé PE, Dorey FJ, et al. Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am 2004;86-A(1):28. 5. Amstutz HC, Le Duff MJ, Campbell PA, et al. Clinical and radiographic results of metal-on-metal hip resurfacing with a minimum ten-year follow-up. J Bone Joint Surg Am 2010;92(16):2663. 6. McMinn DJ, Daniel J, Ziaee H, et al. Indications and results of hip resurfacing. Int Orthop 2011;35(2):231. 7. Langton DJ, Joyce TJ, Jameson SS, et al. Adverse reaction to metal debris following hip resurfacing: the influence of component type, orientation and volumetric wear. J Bone Joint Surg (Br) 2011;93(2):164. 8. Freeman MA, Swanson SA, Heath JC. Study of the wear particles produced from cobalt–chromium–molybdenum–manganese total joint replacement prostheses. Ann Rheum Dis 1969;28(Suppl 5):29. 9. Ladon D, Doherty A, Newson R, et al. Changes in metal levels and chromosome aberrations in the peripheral blood of patients after metal-on-metal hip arthroplasty. J Arthroplasty 2004;19(8 Suppl 3):78. 10. Papageorgiou I, Yin Z, Landon D, et al. Genotoxic effects of particles of surgical cobalt chrome alloy on human cells of different age in vitro. Mutat Res 2007;619(1–2):45. 11. Tsaousi A, Jones E, Case CP. The in vitro genotoxicity of orthopaedic ceramic (Al2O3) and metal (CoCr alloy) particles. Mutat Res 2010;697(1–2):1.
12. Vendittoli PA, Roy AG, Mottard S, et al. Metal ion release from bearing wear and corrosion with 28 mm and large-diameter metal-on-metal bearing articulations: a follow-up study. J Bone Joint Surg (Br) 2010;92(1):12. 13. Vendittoli PA, Amzica T, Roy AG, et al. Metal Ion release with large-diameter metalon-metal hip arthroplasty. J Arthroplasty 2011;26(2):282. 14. Paustenbach DJ, Galbraith DA, Finley BL. Interpreting cobalt blood concentrations in hip implant patients. Clin Toxicol (Phila) 2013;52(2):98–112. 15. Delaunay C, Petit I, Learnmonth ID, et al. Metal-on-metal bearings total hip arthroplasty: the cobalt and chromium ions release concern. Orthop Traumatol Surg Res 2010;96(8):894. 16. M.M.a.H.P.R.. All metal-on-metal (MOM) hip replacement; 2012. 17. Brouwers EE, Tibben M, Rosing H, et al. The application of inductively coupled plasma mass spectrometry in clinical pharmacological oncology research. Mass Spectrom Rev 2008;27(2):67. 18. Sonke JE, Salters VJ. Capillary electrophoresis-high resolution sector field inductively coupled plasma mass spectrometry. J Chromatogr A 2007;1159(1–2):63. 19. Vendittoli PA, Rivière C, Roy AG, et al. Metal-on-metal hip resurfacing compared with 28-mm diameter metal-on-metal total hip replacement: a randomised study with six to nine years' follow-up. Bone Joint J 2013;95-B(11):1464. 20. Lavigne M, Belzile EL, Roy AG, et al. Comparison of whole-blood metal ion levels in four types of metal-on-metal large-diameter femoral head total hip arthroplasty: the potential influence of the adapter sleeve. J Bone Joint Surg Am 2011;93(Suppl 2):128. 21. Case CP, Langkamer VG, James C, et al. Widespread dissemination of metal debris from implants. J Bone Joint Surg (Br) 1994;76(5):701. 22. De Haan R, Pattyn C, Gill HS, et al. Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement. J Bone Joint Surg (Br) 2008;90(10):1291. 23. MacDonald SJ, Brodner W, Jacobs JJ. A consensus paper on metal ions in metal-onmetal hip arthroplasties. J Arthroplasty 2004;19(8 Suppl 3):12. 24. De Smet KA, Van Der Straeten C, Van Oursow M, et al. Revisions of metal-on-metal hip resurfacing: lessons learned and improved outcome. Orthop Clin North Am 2011;42(2):259 [ix]. 25. Grammatopolous G, Pandit H, Kwon YM, et al. Hip resurfacings revised for inflammatory pseudotumour have a poor outcome. J Bone Joint Surg (Br) 2009;91 (8):1019. 26. Case CP, Ellis L, Turner JC, et al. Development of a routine method for the determination of trace metals in whole blood by magnetic sector inductively coupled plasma mass spectrometry with particular relevance to patients with total hip and knee arthroplasty. Clin Chem 2001;47(2):275. 27. Estey MP, Diamandis EP, Van Der Straeten C, et al. Cobalt and chromium measurement in patients with metal hip prostheses. Clin Chem 2013;59(6):880. 28. Barry J, Lavigne M, Vendittoli PA. Evaluation of the method for analyzing chromium, cobalt and titanium ion levels in the blood following hip replacement with a metalon-metal prosthesis. J Anal Toxicol 2013;37(2):90.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Whole blood metal ion measurement reproducibility between different laboratories Michel Rahmé, MD a, Martin Lavigne, MD, MSc b, Janie Barry, MSc b, Ciprian Mihai Cirtiu, PhD c, Patrick Bélanger, MSc c, Pascal-André Vendittoli, MD, MSc b, ⁎ a b c
Hôpital de Hautepierre, Strasbourg, France Hôpital Maisonneuve-Rosemont, Montréal, Québec, Canada Centre de toxicologie du Québec, Institut National de Santé Publique du Québec, Sainte-Foy, Québec, Canada
a r t i c l e
i n f o
Article history: Received 10 January 2014 Accepted 19 July 2014 Keywords: metal ion hip arthroplasty chromium cobalt
a b s t r a c t Monitoring patients' metal ion blood concentrations can be useful in cases of problematic metal on metal hip implants. Our objective was to evaluate the reproducibility of metal ion level values measured by two different laboratories. Whole blood samples were collected in 46 patients with metal on metal hip arthroplasty. For each patients, two whole blood samples were collected and analyzed by two laboratories. Laboratory 1 had higher results than laboratory 2. There was a clinically significant absolute difference between the two laboratories, above the predetermined threshold, 35% of Cr samples and 38% of Co samples. All laboratories do not use the same technologies for their measurements. Therefore, decision to revise a metal on metal hip arthroplasty should rely on metal ion trends and have to be done in the same laboratory. © 2014 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) has proven to be a highly effective treatment of hip osteoarthritis in the elderly which is the reason indications were subsequently extended to young and middle-aged adults as well. Increasing demands in these patient groups due to significant physical activity and higher life expectancy resulted in developing improved bearing materials. These bearings are characterized by potential combinations of highly cross-linked polyethylene, ceramic, or metal cup inserts with ceramic or metal heads. Metal-on-metal (MoM) bearings have been used with conventional THA for several decades with promising results from early applications [1–3]. Low wear potential of mechanically well investigated prostheses, no relevant risk of material fracture, excellent stability and a high design variability seemed to justify the application of MoM bearings in hip resurfacing (HR) and large head hip arthroplasty (LH-THA) [4–6]. Nevertheless, wear and corrosion of these implants may lead to a release of metal products including chromium (Cr) and cobalt (Co) into surrounding tissue and body fluids as well as internal organs. Metal accumulation may result in local “adverse reactions to metal debris” (ARMD) [7] and potentially induce systemic adverse effects (i.e. toxicity, teratogenicity and carcinogenicity) [8–11]. Although the toxicological significance of local and systemic elevations in metal ions has not been definitively established, monitoring patients with MoM bearings for elevated metal ion concentrations in the blood can The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.07.018. Reprint requests: Pascal-A Vendittoli MD, MSc, FRCS, Hôpital MaisonneuveRosemont, 5415 Boul L'Assomption, Montréal, Québec, H1T 2M4 Canada. http://dx.doi.org/10.1016/j.arth.2014.07.018 0883-5403/© 2014 Elsevier Inc. All rights reserved.
be useful in determining the performance of the bearing[12–14]. Metal ions from the corresponding alloying element (i.e. cobalt—Co, chromium —Cr, titanium—Ti, nickel—Ni, molybdenum—Mo) can be measured in the joint itself as well as in surrounding tissue and body fluids. Blood concentrations of ions released from well performing metal implants are low, often less than 1 μg/L [15]. Recent guidelines and metal ion level threshold values have been recently recommended to follow patients with metal and metal bearings THA [16]. As example, the UK Medicines and Healthcare products Regulatory Agency has issued a blood cobalt guidance value of 7 μg/L to identify MoM hip implant patients who may require closer surveillance due to an association with excessive implant wear. High-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) is one of the most sensitive and versatile techniques available for metal ions measurement and most clinicians are relying on results obtained with this analysis method [17,18]. The objective of this study was to evaluate whole blood metal ion levels drawn for the same patient at the same time, but analyzed in two different laboratories. The aim was to see if there was a difference between the laboratories that may be of clinical significance and that could lead to misinterpretation in the results. Material and Methods Study Population From July 2003 and October 2009, we collected whole blood samples in multiple patients with unilateral MoM hip arthroplasty.
M. Rahmé et al. / The Journal of Arthroplasty 29 (2014) 2214–2218
Many of these patients were taking part in structured research protocols with subsequent publications [12,13,19,20]. For the purpose of the present study, patients were eligible when at least two tubes of whole blood from the same collection time were available. Sample Collection For each patient, after discarding the first 5 cc of blood, three whole blood samples were collected in individual polypropylene syringes. For all procedures a twenty-two gauge stainless steel needle (BD Vialon Biomaterial IV catheter, 0.9 × 25 mm, 35 cc/min; Beckton Dickinson, Mississauga, Ontario) were used to cannulate the vein and the outer plastic cannula was left in place while the needle was discarded. All samples were transferred to individual polypropylene tubes (Lavander, K2 EDTA 7.2 mg for laboratory 1 and Royal blue, trace element K2 EDTA 10.8 mg for laboratory 2) and kept frozen at − 20 °C. Patients were asked to not modify their exercises routine or engage in new, strenuous activities, take new medications or undergo other venous sampling 1 week before blood collection. Samples were kept frozen at − 20 °C until analysis by the two different laboratories. Samples were analyzed from December 2011 to April 2013 for laboratory 1 and from March to June 2013 for laboratory 2. Laboratory 1 Analysis, ICP-MS The concentrations of Cr and Co ions in whole blood samples were measured with a single quadrupole ICP-MS Elan DRCII from PerkinElmer. The detection limits were 0.1 μg/L for Cr and 0.035 μg/L for Co. Blood samples were diluted in diluent containing 0.5% (v/v) NH4OH and 0.1% (v/v) octylphenol ethoxylate. External calibration curves were prepared by diluting human blood in diluent and spiking with different volumes of 1 mg L −1 multi-elements standard solution (SCP Science, PlasmaCal ICP-MS Verification Standard 1, 5% HNO3, #141-110-011) in order to emulate 0, 4, 20, 80, and 200 μg/L in the standards solutions. The internal standard for calibration standards and blood samples was yttrium 89 for Co59 (standard mode with correction equation) and indium 115 for Cr53 (DRC mode with ammonia as reaction gas). Commercial blood reference materials were used as controls to verify the results. Laboratory 2 Analysis, HR-ICP-MS The concentrations of Cr and Co ions in the whole blood samples were measured in an Element 2 High-Resolution, Sector-Field, Inductively Coupled Plasma Mass Spectrophotometer (Thermo Fisher Scientific GmBH, Bremen, Germany). The detection limits were 0.1 μg/L for Cr and 0.02 μg/L for Co. The blood samples were exposed to concentrated nitric acid to digest protein and concentrated hydrogen peroxide to digest lipids. After dilution with water and internal standard yttrium 89, the final sample was introduced into the instrument and compared against aqueous standards with commercial blood controls to verify the results. Statistical Significance The detection limit of the HR-ICP-MS is approximately 3 times the background noise of the samples. The limit of quantification, which determines more precisely the sensitivity and accuracy of the device, is approximately 10 times the background noise. The limit of quantification is therefore 3.33 times the limit of detection. For this study, we have used the very specific detection limit of the HR-ICP-MS used in laboratory 2 (0.1 μg/L and 0.02 μg/L for Cr and Co in whole blood) to establish the limit of quantification. Based on these values, we determined that a conservative difference of 3.5 times the detection limit will be considered statistically significant or 0.35 μg/L for Cr and 0.07 μg/L for Co.
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Clinical Significance We defined in a previous study that a variation in concentration above 1 μg/L for Cr and above 0.5 μg/L for Co could be clinically significant. These thresholds were established based on the average concentrations of Cr and Co varying between 0.5 and 3 μg/L in blood when implants are working well. In the event of a malfunction or clinical problem, the concentration of these ions usually increases dramatically from 2 to 20 μg/L. So, according to the authors, a variation in concentration of less than 1 μg/L for Cr and less than 0.5 μg/L for Co between results would not impact the clinical evaluation and patients follow up. Statistical Analysis Statistical analysis was performed using SPSS software, version 20.0. All patients with paired results were included in the study. Continuous values were presented as an average ± standard deviation with minimum and maximum values. Differences between pairs of sample were analyzed by a paired t-test with a confidence interval of 95%. Differences between pairs of samples (in absolute values) were analyzed by a simple t-test with a confidence interval of 95%. Proportion tests were performed with a chi-square test. Correlations between results of laboratories were analyzed with Pearson correlation. The difference between the reproducibility (mean difference) of the measure of chromium and cobalt metal ions was analyzed by Student's t-test for independent data. Statistical significance was set at 0.05. Ethical Considerations The research project was approved by the Scientific Committee and the Ethics Committee of our Centre. The study was explained to patients and informed consent was obtained. Results We have analyzed a total of 46 pairs of whole blood samples. Patient's mean age at the surgery was 50 years (range 28–65) and there were 24 men and 22 women. Thirty-six patients had large diameter femoral head THA, 9 patients a hip resurfacing (HR) and 1 patient a 28 mm THA. Fifty-one percent of hip implants were made by Zimmer, 18% by Biomet, 11% by Depuy and 20% by Smith Nephew. The mean follow-up at the blood collection time was 63 months (range 12–96). Samples were kept frozen for an average of 0.11 months (min 0, max 0.39 months) before analysis at laboratory 1 and 5.33 months (min 0.1, max 16.16) at laboratory 2. The distributions of Cr and Co concentrations from the two different laboratories are shown in Fig. 1 and Table 1. The concentrations obtained from laboratory 1 are significantly different than from laboratory 2. Table 2 and Fig. 2 show the distribution of differences between the two laboratories. Laboratory 1 had higher result than laboratory 2 with a CI (95%) of 0.30 to 1.23 for Cr and 0.12 to 0.93 for Co. The results of laboratory 1 were higher than those of laboratory 2 in 70 and 82% for Cr and Co respectively. The mean ratios between laboratory 1 and 2 are 1.30 (range 0.37 to 4.28) and 1.14 (range 0.46 to 2.12) for Cr and Co respectively. The distribution of absolute difference between the laboratories is shown in Table 3 and Fig. 3. The means absolute difference between the two laboratories was significant for Cr and Co metal ions measured. Thirty-five percent of paired samples for Cr and 38% for Co had an absolute difference above the predetermined threshold of clinical significance. We found a high statistical correlation between the laboratories for Cr (0.841) and Co (0.965) measured (P ≤ 0.001 for Cr and Co). The Bland and Altman graph, shown in Figs. 4 and 5, established that the
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M. Rahmé et al. / The Journal of Arthroplasty 29 (2014) 2214–2218 Table 2 Mean Differences (Laboratory 1–Laboratory 2) and Thresholds of Clinical Significance for Cr and Co.
Ion
n
Mean difference (μg/L) a
Standard deviation
Cr Co
46 45
0.76 [−2.62 to 7.32] 0.52 [3.15 to 4.99]
1.57 1.35
a
Fig. 1. Box plot of the concentration of Cr and Co metal ions in the two laboratories. Horizontal bars define the quartiles, with the second and third quartiles contained in the boxes. Circles represent outliers, defined as values that are 1.5 to 3 times higher than the values of the third quartile. The data identified with stars are extreme outliers, defined as values that are at least three times higher than the values of the third quartile.
agreement limits of Cr and Co measures are over the predetermined threshold of clinical significance. Furthermore, we did not find any significant difference between the reproducibility (mean difference) of the measure of Cr and Co metal ions (P = 0.441). Discussion
P-value 0.002 0.012
Threshold of clinical significance 1.0 0.5
Results are shown as the mean with minimum and maximum in square brackets.
measured by two different laboratories using similar analysis methods. Inter laboratory reproducibility for metal ion measurements in patients who underwent MoM THA is important as patients may travel from one surgeon to another or can be screened in different reference centers. The surgeon has to know if results coming from different laboratories can be reliable. Comparing 46 pairs of samples taken in the same patients and analyzed by two different laboratories, we found a statistical difference between the results (Table 1). The mean absolute difference was significant for Cr and Co metal ions measured and 35% of paired samples for Cr and 38% for Co had an absolute difference above the predetermined threshold of clinical significance (Table 3). The results of laboratory 1 were higher than those of laboratory 2 in 70 and 82% for Cr and Co respectively (Table 2). Regarding the ion analysis method, HR-ICP-MS has already been proven to be the gold standard method in metal ion analysis even though some laboratories still use atomic absorption spectrometry (AAS) [15,17,18]. In our study both laboratories were equipped with ICP-MS instruments, with the difference being that only laboratory 2 had a high resolution instrument. A high resolution device allows to discard some spectral interferences that are common with an ICP-MS analysis technology. Polyatomic interferences are known to occur in analysis by ICP-MS. However, when an analysis is directed to trace or ultratrace concentrations of metals, possible interferences that appeared to be insignificant or nonexistent can have an important impact on the validity of the analysis [26]. However not all subjects have interferences which could explain why the differences between the two laboratories are not systematic.
Metal-on-metal (MoM) bearings have been used with hip arthroplasty for several decades with promising results from early applications. Nevertheless, wear and corrosion of these implants lead to local and systemic metal products release. Monitoring patients' metal ion blood concentrations can be useful in determining the performance of the bearing and indicating need for revision surgery for problematic implants [21,22]. The level proposed as the indicator of well functioning small-diameter metal-on-metal THAs is 1 μg/L [23]. As some MoM implant may present higher than expected wear and metal ions release after implantation, clinical follow up and systemic metal ion release in patients' blood or serum were advised. Metal ion measurements allow the early detection of increased wear before extensive tissue destruction has occurred with a better outcome of revisions. Some authors and the National Institute recently proposed additional investigations and/or bearing revision when Cr and/or Co levels exceed 7 μg/L [24,25]. The objective of our study was to evaluate the reproducibility of metal ion levels values
Table 1 Distribution of the Concentrations of Cr and Co Metal Ions in Laboratories 1 and 2.
Ions Chromium Cobalt
Laboratory n 1 2 1 2
46 45
Minimum Maximum Average Standard P(μg/L) (μg/L) (μg/L) deviation value 0.45 0.46 0.35 0.29
13.01 6.71 17.68 13.55
3.04 2.27 4.51 3.98
2.65 1.59 4.50 3.67
0.002 0.012
Fig. 2. Box plot of the difference in concentration of Cr and Co metal ions for the two laboratories. Horizontal bars define the quartiles, with the second and third quartiles contained in the boxes. Circles represent outliers, defined as values that are 1.5 to 3 times higher than the values of the third quartile. The data identified with stars are extreme outliers, defined as values that are at least three times higher than the values of the third quartile.
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Table 3 Mean Absolute Differences and Thresholds of Clinical Significance for Cr and Co in Two Different Laboratories.
Ion
n
Mean absolute difference (μg/L)
Cr Co
46 45
1.11 [0.01–7.32] 0.82 [0.01–4.99]
a
a
Standard deviation
P-value
Threshold of clinical significance
1.34 1.20
≤0.001 ≤0.001
1.0 0.5
Results are shown as the mean with minimum and maximum in square brackets.
Other variables can be taken into account for explaining the differences between the results of the two laboratories such as sample contamination, stability of the sample over time as well as the sampling protocol and the method itself. It is well known that Cr and Co are present as stabilizers and coloring agents in rubber products (stoppers, plunger seals) [27]. It has to be noticed that despite the fact that the samples were collected at the same time, the analyses were done at different times by the two laboratories, with gaps ranging from 1 to 18 months. Furthermore, the samples were collected in two different types of tubes. The first tube, containing 10.8 mg K2 EDTA (Royal blue trace elements) was sent to laboratory 2 while the second one, which had 7.2 mg K2 EDTA (Lavender) was sent to laboratory 1. This difference in the quantity of anticoagulant can be at the basis of matrix effects which could explain the disagreement between the results of the two laboratories. Moreover, the sample preparation prior to analysis is very different for both laboratories. Laboratory 1 proceeds through a simple dilution of the blood sample with a basic diluent combined with a matrix matched calibration while the procedure of laboratory 2 involves digestion of the samples and an aqueous calibration. This main difference could explain the differences observed between the laboratories. We also published recently the reproducibility of samples analyzed by the same laboratory [28]. The laboratory did blind analyses of 78 pairs of whole blood samples taken at the same time in the same patients. The absolute difference between the two samples was greater than the limit of quantification of the HR-ICP-MS device
Fig. 3. Box plot of the absolute difference in concentration of Cr and Co metal ions for the two laboratories. Horizontal bars define the quartiles, with the second and third quartiles contained in the boxes. Circles represent outliers, defined as values that are 1.5 to 3 times higher than the values of the third quartile. The data identified with stars are extreme outliers, defined as values that are at least three times higher than the values of the third quartile.
Fig. 4. Bland–Altman plot between chromium concentrations obtained in two different laboratories. The solid line indicates the mean difference (or bias); the dotted lines indicate the 95% limits of the agreement.
for all three ions (0.84 versus 0.35 mg/L for Cr, 0.74 versus 0.07 for Co, and 0.88 versus 0.70 mg/L for Ti). Although the levels were very small in most cases, they exceeded the clinical significant threshold in 19 to 31% of the cases. Given the results we had in this intra observer reproducibility study and the current one showing mismatch between two laboratories, as over 30% of the samples clinicians should be aware of such limited intra and inter laboratory reproducibility. Even though variations are not major, they are significant enough to risk misinterpretation in borderline cases for which revision surgery might be considered. This has to be taken into account when assessing a patient who had his previous metal ion measurements done in another laboratory. Results must whenever possible be compared to results from the same laboratory to avoid the risk of misinterpreting inter-laboratory variations. Moreover, it is important to base our clinical decision on a metal ion unfavorable trend over a certain period and not on a simple elevated measure. Absolute values taken out of context are less meaningful. This is why we recommend having the measurements done in the same laboratory, so that the values obtained are as accurate as possible.
Fig. 5. Bland–Altman plot between the cobalt concentrations obtained in two different laboratories. The solid line indicates the mean difference (or bias); the dotted lines indicate the 95% limits of the agreement.
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Conclusion Ion metal blood screening is a common way of detecting malfunctioning MoM hip arthroplasty, in association with clinical and radiological findings. However, all laboratories do not use the same technologies or calibrations to do these measurements. Even though variations are not major, we found that they are significant enough in more than 1/3 of the cases to risk misinterpretation in borderline cases. Therefore, decision to revise a metal on metal hip arthroplasty should not rely on a simple metal ion measurement and should include patient symptoms and radiographic evidences of implant dysfunction. References 1. Dorr LD, Wan Z, Dubois B, et al. Total hip arthroplasty with use of the Metasul metal-on-metal articulation. Four to seven-year results. J Bone Joint Surg Am 2000; 82(6):789. 2. Wagner M, Wagner H. Medium-term results of a modern metal-on-metal system in total hip replacement. Clin Orthop Relat Res 2000;379:123. 3. Weber BG. Experience with the Metasul total hip bearing system. Clin Orthop Relat Res 1996(329 Suppl):S69. 4. Amstutz HC, Beaulé PE, Dorey FJ, et al. Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am 2004;86-A(1):28. 5. Amstutz HC, Le Duff MJ, Campbell PA, et al. Clinical and radiographic results of metal-on-metal hip resurfacing with a minimum ten-year follow-up. J Bone Joint Surg Am 2010;92(16):2663. 6. McMinn DJ, Daniel J, Ziaee H, et al. Indications and results of hip resurfacing. Int Orthop 2011;35(2):231. 7. Langton DJ, Joyce TJ, Jameson SS, et al. Adverse reaction to metal debris following hip resurfacing: the influence of component type, orientation and volumetric wear. J Bone Joint Surg (Br) 2011;93(2):164. 8. Freeman MA, Swanson SA, Heath JC. Study of the wear particles produced from cobalt–chromium–molybdenum–manganese total joint replacement prostheses. Ann Rheum Dis 1969;28(Suppl 5):29. 9. Ladon D, Doherty A, Newson R, et al. Changes in metal levels and chromosome aberrations in the peripheral blood of patients after metal-on-metal hip arthroplasty. J Arthroplasty 2004;19(8 Suppl 3):78. 10. Papageorgiou I, Yin Z, Landon D, et al. Genotoxic effects of particles of surgical cobalt chrome alloy on human cells of different age in vitro. Mutat Res 2007;619(1–2):45. 11. Tsaousi A, Jones E, Case CP. The in vitro genotoxicity of orthopaedic ceramic (Al2O3) and metal (CoCr alloy) particles. Mutat Res 2010;697(1–2):1.
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