Creatinine Assay Attainment of Analytical Performance Goals Following Implementation of IDMS Standardization: Further Improvements Required.
BACKGROUND
The international initiative to standardize creatinine (Cr) assays by tracing reference materials to Isotope Dilution Mass Spectrometry (IDMS) assigned values was implemented to reduce interlaboratory variability and improve assay accuracy.


OBJECTIVE
The aims of this study were to examine whether IDMS standardization has improved Cr assay accuracy (bias), interlaboratory variability (precision), total error (TE), and attainment of recommended analytical performance goals.


METHODS
External Quality Assessment (EQA) data (n = 66 challenge vials) from Ontario, Canada, were analyzed. The bias, precision, TE, and the number of EQA challenge vials meeting performance goals were determined by assay manufacturer before (n = 32) and after (n = 34) IDMS implementation.


RESULTS
The challenge vials with the worst bias and precision were spiked with known common interfering substances (glucose and bilirubin). IDMS standardization improved assay bias (10.4%-1.6%,P< .001), but precision remained unchanged (5.0%-4.7%,P= .5) with performance goals not consistently being met. Precision and TE goals based on biologic variation were attained by only 29% to 69% and 32% to 62% of challenge vials.


CONCLUSIONS
While IDMS standardization has improved Cr assay accuracy and thus reduced TE, significant interlaboratory variability remains. Contemporary Cr assays do not currently meet the standards required to allow for accurate and consistent estimated glomerular filtration rate assessment and chronic kidney disease diagnosis across laboratories. Further improvements in Cr assay performance are needed.
Division of Nephrology, Department of Medicine, Queen's University, Kingston, Ontario, Canada.
Elizabeth Sunmin
ES
Lee
Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada.
Christine P
CP
Collier
Division of Nephrology, Department of Medicine, Queen's University, Kingston, Ontario, Canada.
Christine A
CA
White
External Quality Assessment; IDMS traceable; chronic kidney disease; creatinine