Anders Grubb1, Masaru Horio2, Lars-Olof Hansson3, Jonas Björk4, Ulf Nyman5, Mats Flodin3, Anders Larsson3, Arend Bökenkamp6, Yoshinari Yasuda2, Hester Blufpand6, Veronica Lindström7, Ingrid Zegers8, Harald Althaus9, Søren Blirup-Jensen7, Yoshi Itoh10, Per Sjöström11, Gunnar Nordin12, Anders Christensson13, Horst Klima14, Kathrin Sunde15, Per Hjort-Christensen16, David Armbruster17, Carlo Ferrero18. 1. Department of Clinical Chemistry, Laboratory Medicine, University Hospital, Lund, Sweden; anders.grubb@med.lu.se. 2. Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Suita, Osaka, Japan; 3. Department of Medical Sciences, Uppsala University, Uppsala, Sweden; 4. Department of Occupational and Environmental Medicine, Lund University, Lund, Sweden; 5. Department of Radiology, Central Hospital, Kristianstad, University of Lund, Sweden; 6. Department of Pediatric Nephrology, VU University Medical Center, Amsterdam, The Netherlands; 7. Department of Clinical Chemistry, Laboratory Medicine, University Hospital, Lund, Sweden; 8. Institute for Reference Materials and Measurements, Joint Research Centre, European Commission, Geel, Belgium; 9. Siemens Healthcare Diagnostics Products GmbH, Marburg, Germany; 10. Department of Laboratory Medicine, EIJU, General Hospital, Tokyo, Japan; 11. Department of Medicine, Örebro University Hospital, Örebro, Sweden; 12. Equalis, Uppsala, Sweden; 13. Department of Nephrology and Transplantation, Skåne University Hospital, Lund, Sweden; 14. Roche Diagnostics GmbH, Penzberg, Germany; 15. Gentian Technology AS, Moss, Norway; 16. Dako Denmark A/S, Glostrup, Denmark; 17. Abbott Diagnostics, Lake Forest, IL; 18. Sentinel CH. SpA, Milan, Italy.
Abstract
BACKGROUND: Many different cystatin C-based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays. METHODS: Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C-based equation for estimation of GFR. RESULTS: We developed a simple cystatin C-based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, [Formula: see text] is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C. CONCLUSIONS: A virtually assay-independent simple cystatin C-based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced.
BACKGROUND: Many different cystatin C-based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays. METHODS: Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C-based equation for estimation of GFR. RESULTS: We developed a simple cystatin C-based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, [Formula: see text] is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C. CONCLUSIONS: A virtually assay-independent simple cystatin C-based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced.
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