Validation of a new standardized cystatin C turbidimetric assay: Evaluation of the three novel CKD-EPI equations in hypertensive patients

Abstract

ObjectivesAnalytical and clinical performances of the new standardized cystatin C particle-enhanced turbidimetric immunoassay (PETIA) using DiaSys reagents on Olympus AU2700® analyzer were evaluated. Design and methodsWe have studied imprecision, linearity, limit of detection and limit of quantification of this new immunoassay. Method comparison was assessed in relation to results generated by the standardized Siemens-particle-enhanced nephelometric immunoassay (PENIA). In order to evaluate the clinical relevance of this assay, estimated glomerular filtration rate (GFR) was calculated using MDRD, CKD-EPI creatinine, CKD-EPI cystatin C 2012 and CKD-EPI creatinine–cystatin C 2012 equations and compared to GFR measured using urinary clearance of 99mTc-DTPA in 100 hypertensive patients. ResultsCystatin C measurements using DiaSys reagents have reliable analytical performances and are comparable to the standardized Siemens-PENIA method (bias of 0.01mg/L). The mean measured GFR was 90.0±29.7mL/min/1.73m2. Bias and accuracy of the three CKD-EPI equations were better than the MDRD. Both CKD-EPI creatinine-based and cystatin C-based formulae had similar bias, precision and accuracy. The combined creatinine–cystatin C equation was significantly more accurate and precise than the CKD-EPI creatinine equation in patients with GFR above 60mL/min/1.73m2. ConclusionsThe use of cystatin C in a combined equation with creatinine could improve the accuracy of eGFR in the reference interval.