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

Objectives: Analytical 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 Methods: We 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 (99m)Tc-DTPA in 100 hypertensive patients.

Results: Cystatin C measurements using DiaSys reagents have reliable analytical performances and are comparable to the standardized Siemens-PENIA method (bias of 0.01 mg/L). The mean measured GFR was 90.0±29.7 mL/min/1.73 m². 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 60 mL/min/1.73 m².

Conclusions: The use of cystatin C in a combined equation with creatinine could improve the accuracy of eGFR in the reference interval.