Original Investigations: Pathogenesis and TreatmentCalibration and random variation of the serum creatinine assay as critical elements of using equations to estimate glomerular filtration rate☆,☆☆,★
Section snippets
Methods
Serum creatinine was measured as part of both the MDRD study (1989 to 1991) and NHANES III (1988 to 1994). Both studies were funded by The National Institutes of Health and reported good quality control, providing an opportunity to show the issues in applying an equation developed for estimating GFR based on serum creatinine assays in one laboratory to serum creatinine assays obtained in another laboratory. Repeated analysis of frozen serum from both studies allows for examination of
Results
Figure 1 shows the comparison of original serum creatinine measurements in the MDRD study to duplicate measurements on thawed samples in the Cleveland Clinic and White Sands laboratories during 2000.
Discussion
Given appropriate calibration of the serum creatinine assay, estimates of GFR can be reproducible (SD of estimates 2 weeks apart, 15%). For example, at moderately decreased GFRs (GFR, 30 to 59 mL/min/1.73 m2), estimates of GFR based on serum creatinine level are precise enough to allow for diagnosis and clinical management. At this GFR range, a follow-up estimated GFR will be within 27% and a measured iothalamate GFR will be within 30% of the original estimate most of the time, corresponding to
Acknowledgements
The authors thank the White Sands and Cleveland Clinic laboratories, which facilitated the conduct of this study by conducting assays and providing access to their quality control data; investigators and participants of the MDRD study and NHANES III, which provided data for this study; as well as their funding institutes, the National Institute of Diabetes, Digestive and Kidney Disease and the National Center for Health Statistics.
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Cited by (0)
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Supported in part by a grant from the National Kidney Foundation as part of the Kidney Disease Outcomes Quality Initiative; and National Institutes of Health grants no. DK48362 and RR00722 (J.C.); grant no. UO1 DK35073 (T.G.); grants no. RO1 DK53869 and UO1 DK35073 (A.S.L.); and grant no. T32HL7024 (B.C.A.).
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Address reprint requests to Josef Coresh, MD, PhD, 2024 E Monument, Baltimore, MD 21205. E-mail: [email protected]
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