Standardization and improvement program for creatinine measurement in human serum

Current practices, quality control systems and proficiency testing schemes in clinical laboratories are likely unable to detect intrinsic bias in the in vitro diagnostic kits for creatinine as characterized or applied. A standardization program for clinical laboratories to determine the concentration of creatinine in human serum prior to estimate the glomerular filtration rate (eGFR) was conducted by the Mexican Association for Prevention of Chronic Diseases (AMPEC) and CENAM in 2016. In this study, 21 public and private clinical laboratories participated voluntarily and contributed with results of 27 measurement methods. These results were used to build a set of specific bias models, respectively, and then applied by each laboratory to correct their new measurements. A two-stage study was conducted; the first stage consisted of a blind experiment using certified reference material (CRM) DMR-574a of creatinine in human serum at three levels. The participating laboratories measured all three CRMs samples under a proficiency testing protocol using their routine methods. Linear regression with error in variables was applied to modeling the participants’ measurement method. In the second stage, each laboratory measured the concentration of creatinine in serum in approximately 100 samples from ambulatory patients, obtaining a total sample of 2416 measurements; subsequently, eGFR was calculated. In most of the participating laboratories (97 %), significant creatinine measurement bias was observed. Diagnosis based only on the concentration of creatinine in serum showed that: 72 % of the cases were correct, 23 % underestimated the eGFR and 5 % overestimated the eGFR. Bias is induced in the eGFR if no correction is made.