Recent Trends in Performance and Current State of Creatinine Assays

Context.—Measured plasma or serum creatinine concentration is a primary component of equations used to calculate estimated glomerular filtration rate (eGFR). In recent years, most assay manufacturers have adopted creatinine calibration procedures that are traceable to the National Institute of Standards and Technology's Standard Reference Material 967. Objectives.—To examine the current performance of creatinine assays, to compare changes in assay performance since 2003, and to examine the reliability of laboratory eGFR calculations. Design.—Serum samples spiked with different concentrations of creatinine were analyzed by participating laboratories in the College of American Pathologists' LN24 survey. Participants' reported values were compared against values measured by liquid chromatography-isotope dilution mass spectrometry. Participants were asked to calculate the eGFR for certain samples, and results were compared with those obtained from the 4-parameter Modification of Diet in Renal Disease equation...