Abstract
Objectives
Sweat chloride testing (SCT) is the mainstay for the diagnosis of cystic fibrosis (CF) and biomarker in the evaluation of CFTR-modifying drugs. To be a reliable and valid tool, analytical variance (CVA) must be minimized. However, external quality assessments have revealed significant deviations in routine clinical practice. Our goal was to identify and quantify technical errors through proficiency testing and simulations.
Methods
Chloride concentrations of three blinded samples (each as triplicates) were measured in 9 CF centers using a chloridometer in a routine setting. Technical errors were simulated and quantified in a series of measurements. We compared imprecision and bias before and after a counseling session by evaluating coefficients of variation (CV), adherence to tolerance limits, and inter-rater variability coefficients.
Results
Pipetting errors resulting in changes in sample volume were identified as the main source of error with deviations up to 41%. After the counseling session, the overall CVA decreased from 7.6 to 5.2%, the pass rate increased from 67 to 92%, and the inter-rater variability diminished. Significant deviations continued to be observed in individual centers.
Conclusions
Prevention of technical errors in SCT decreases imprecision and bias. Quality assurance programs must be established in all CF centers, including staff training, standard operating procedures, and proficiency testing.
Acknowledgments
The authors would like to thank Jana Streller and Anett Kiesel for managing the chloride measurements.
Research funding: None declared.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Authors state no conflict of interest.
Informed consent: Not applicable.
Ethical approval: The local Institutional Review Board deemed the study exempt from review.
References
1. Farrell, PM, White, TB, Ren, CL, Hempstead, SE, Accurso, F, Derichs, N, et al.. Diagnosis of cystic fibrosis: consensus guidelines from the cystic fibrosis foundation. J Pediatr 2017;181S:S4–15.e1. https://doi.org/10.1016/j.jpeds.2016.09.064.Search in Google Scholar
2. Muhlebach, MS, Clancy, JP, Heltshe, SL, Ziady, A, Kelley, T, Accurso, F, et al.. Biomarkers for cystic fibrosis drug development. J Cyst Fibros 2016;15:714–23. https://doi.org/10.1016/j.jcf.2016.10.009.Search in Google Scholar
3. Collaco, JM, Blackman, SM, Raraigh, KS, Corvol, H, Rommens, JM, Pace, RG, et al.. Sources of variation in sweat chloride measurements in cystic fibrosis. Am J Respir Crit Care Med 2016;194:1375–82. https://doi.org/10.1164/rccm.201603-0459OC.Search in Google Scholar
4. Naehrlich, L. Sweat testing practices in German cystic fibrosis centres. Klin Padiatr 2007;219:70–3. https://doi.org/10.1055/s-2007-872458.Search in Google Scholar
5. Mackay, R, George, P, Kirk, J. Sweat testing for cystic fibrosis: a review of New Zealand laboratories. J Paediatr Child Health 2006;42:160–4. https://doi.org/10.1111/j.1440-1754.2006.00822.x.Search in Google Scholar
6. Cirilli, N, Southern, KW, Buzzetti, R, Barben, J, Nährlich, L, Munck, A, et al.. Real life practice of sweat testing in Europe. J Cyst Fibros 2017. https://doi.org/10.1016/j.jcf.2017.09.002.Search in Google Scholar
7. LeGrys, VA. Sweat analysis proficiency testing for cystic fibrosis. Pediatr Pulmonol 2000;30:476–80. https://doi.org/10.1002/1099-0496(200012)30:6<476::aid-ppul7>3.0.co;2-o.10.1002/1099-0496(200012)30:6<476::AID-PPUL7>3.0.CO;2-OSearch in Google Scholar
8. Salvatore, M, Floridia, G, Amato, A, Censi, F, Stefano, MCde, Ferrari, G, et al.. Italian external quality assessment program for cystic fibrosis sweat chloride test: a 2015 and 2016 results comparison. Ann Ist Super Sanita 2017;53:305–13. https://doi.org/10.4415/ANN_17_04_06.Search in Google Scholar
9. Aralica, M, Krleza, JL. Evaluating performance in sweat testing in medical biochemistry laboratories in Croatia. Biochem Med (Zagreb) 2017;27:122–30. https://doi.org/10.11613/BM.2017.016.Search in Google Scholar
10. Plebani, M. Errors in clinical laboratories or errors in laboratory medicine? Clin Chem Lab Med 2006;44:750–9. https://doi.org/10.1515/CCLM.2006.123.Search in Google Scholar
11. LeGrys, VA, Moon, TC, Laux, J, Rock, MJ, Accurso, F. Analytical and biological variation in repeated sweat chloride concentrations in clinical trials for CFTR modulator therapy. J Cyst Fibros 2018;17:43–9. https://doi.org/10.1016/j.jcf.2017.07.008.Search in Google Scholar
12. Plebani, M, Padoan, A, Lippi, G. Biological variation: back to basics. Clin Chem Lab Med 2015;53:155–6. https://doi.org/10.1515/cclm-2014-1182.Search in Google Scholar
13. CLSI. Sweat testing: specimen collection and quantitative sweat testing: specimen collection and quantitative chloride analysis. 4th ed. CLSI guideline C34. Wayne, PA: Clinical and Laboratory Standards Institute; 2019.Search in Google Scholar
14. Guidelines for the Performance of the Sweat Test for the Investigation of Cystic Fibrosis in the UK. An Evidence Based Guideline. 2nd Version; 2014.Search in Google Scholar
15. Massie, J, Greaves, R, Metz, M, Wiley, V, Graham, P, Shepherd, S, et al.. Australasian guideline (2nd Edition): an annex to the CLSI and UK guidelines for the performance of the sweat test for the diagnosis of cystic fibrosis. Clin Biochem Rev 2017;38:115–30.Search in Google Scholar
16. The College of American Pathologists. Excerpt from SW-A 2015 PSR, specimen SW-02. Available from: https://documents.cap.org/documents/2015-b-sweat-analysis-survey.pdf [Accessed 10 Dec 2020].Search in Google Scholar
17. Fraser, CG. Inherent biological variation and reference values. Clin Chem Lab Med 2004;42:758–64. https://doi.org/10.1515/CCLM.2004.128.Search in Google Scholar
18. LeGrys, VA, Moon, TC, Laux, J, Accurso, F, Martiniano, SA. A multicenter evaluation of sweat chloride concentration and variation in infants with cystic fibrosis. J Cyst Fibros 2019;18:190–3. https://doi.org/10.1016/j.jcf.2018.12.006.Search in Google Scholar
19. LeGrys, VA, McColley, SA, Li, Z, Farrell, PM. The need for quality improvement in sweat testing infants after newborn screening for cystic fibrosis. J Pediatr 2010;157:1035–7. https://doi.org/10.1016/j.jpeds.2010.07.053.Search in Google Scholar
20. Kharrazi, M, Milla, C, Wine, J. Sweat chloride testing: controversies and issues. Lancet Respir Med 2016;4:605–7. https://doi.org/10.1016/S2213-2600(16)30182-5.Search in Google Scholar
21. Wielpütz, MO, Puderbach, M, Kopp-Schneider, A, Stahl, M, Fritzsching, E, Sommerburg, O, et al.. Magnetic resonance imaging detects changes in structure and perfusion, and response to therapy in early cystic fibrosis lung disease. Am J Respir Crit Care Med 2014;189:956–65. https://doi.org/10.1164/rccm.201309-1659OC.Search in Google Scholar
22. Stahl, M, Wielpütz, MO, Ricklefs, I, Dopfer, C, Barth, S, Schlegtendal, A, et al.. Preventive inhalation of hypertonic saline in infants with cystic fibrosis (PRESIS): a randomized, double-blind, controlled study. Am J Respir Crit Care Med 2018. https://doi.org/10.1164/rccm.201807-1203OC.Search in Google Scholar
23. Sly, PD, Brennan, S, Gangell, C, Klerk, Nde, Murray, C, Mott, L, et al.. Lung disease at diagnosis in infants with cystic fibrosis detected by newborn screening. Am J Respir Crit Care Med 2009;180:146–52. https://doi.org/10.1164/rccm.200901-0069OC.Search in Google Scholar
24. Conway, S, Balfour-Lynn, IM, Rijcke, Kde, Drevinek, P, Foweraker, J, Havermans, T, et al.. European cystic fibrosis Society standards of care: framework for the cystic fibrosis centre. J Cyst Fibros 2014;13:S3–22. https://doi.org/10.1016/j.jcf.2014.03.009.Search in Google Scholar
25. CLSI. Sweat testing: specimen collection and quantitative chloride analysis; approved guideline, 3rd ed. CLSI document C34-A3. Wayne, PA: Clinical and Laboratory Standards Institute; 2009.Search in Google Scholar
26. Bundesärztekammer. Neufassung der „Richtlinie der Bundesärztekammer zur Qualitätssicherung laboratoriumsmedizinischer Untersuchungen – “Rili-BÄK“. Deutsches Ärzteblatt 2014;111:1583–618.Search in Google Scholar
27. Carrasco, JL, Martinez, JP. Concordance correlation coefficient for repeated (and non-repeated) measures. Package cccrm; 2015. Available from: ftp://mirrors.ucr.ac.cr/CRAN/web/packages/cccrm/cccrm.pdf [Accessed 23 Apr 2019].Search in Google Scholar
28. Lin, L. Overview of agreement statistics for medical devices. J Biopharm Stat 2008;18:126–44. https://doi.org/10.1080/10543400701668290.Search in Google Scholar
29. McBride, GB. A proposal for strength-of-agreement criteria for Lin’s concordance correlation coefficient. NIWA Project MOH05201, NIWA client report. Hamilton, New Zealand: National Institute of Water and Atmospheric Research Ltd; 2005:HAM2005-062 p.Search in Google Scholar
30. DeMarco, ML, Dietzen, DJ, Brown, SM. Sweating the small stuff: adequacy and accuracy in sweat chloride determination. Clin Biochem 2015;48:443–7. https://doi.org/10.1016/j.clinbiochem.2014.12.011.Search in Google Scholar
31. LeGrys, VA, Yankaskas, JR, Quittell, LM, Marshall, BC, Mogayzel, PJ. Diagnostic sweat testing: the cystic fibrosis foundation guidelines. J Pediatr 2007;151:85–9. https://doi.org/10.1016/j.jpeds.2007.03.002.Search in Google Scholar
32. Salvatore, M, Floridia, G, Amato, A, Censi, F, Carta, C, Stefano, MCde, et al.. The Italian pilot external quality assessment program for cystic fibrosis sweat test. Clin Biochem 2016;49:601–5. https://doi.org/10.1016/j.clinbiochem.2015.12.014.Search in Google Scholar
33. Salvatore, M, Floridia, G, Amato, A, Censi, F, Carta, C, Stefano, MCde, et al.. The Italian external quality assessment program for CF sweat chloride test: results of the 2015 round. J Chromatogr B 2016;4:33–43. https://doi.org/10.15640/jcb.v4n2a4.Search in Google Scholar
34. Cirilli, N, Braggion, C, Mergni, G, Polizzi, AM, Padoan, R, Sirianni, S, et al.. May the new suggested lower borderline limit of sweat chloride impact the diagnostic process for cystic fibrosis? J Pediatr 2018;194:261–2. https://doi.org/10.1016/j.jpeds.2017.11.053.Search in Google Scholar
Supplementary Material
The online version of this article offers supplementary material (https://doi.org/10.1515/cclm-2020-1661).
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