GFR estimation using standardized serum cystatin C in Japan

Area of Science:

• Nephrology
• Biomarkers
• Epidemiology

Background:

• The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) developed equations to estimate glomerular filtration rate (GFR) using standardized serum cystatin C (CKD-EPI(cys)) and a combination of creatinine and cystatin C (CKD-EPI(cr-cys)).
• There is a need to evaluate and potentially adapt these equations for diverse populations, such as the Japanese population.

Purpose of the Study:

• To develop and validate new GFR-estimating equations based on standardized serum cystatin C specifically for the Japanese population.
• To compare the accuracy of these novel Japanese equations against existing CKD-EPI equations.

Main Methods:

• A diagnostic accuracy study was conducted using development (n=413) and validation (n=350) datasets.
• New Japanese equations were developed using standardized cystatin C (Eq(cys)), cystatin C with a nonrenal factor (Eq(cys+nonrenal)), and creatinine with cystatin C (Eq(cr-cys)).
• Measured GFR by inulin renal clearance served as the reference standard.

Main Results:

• Japanese coefficients were derived for CKD-EPI(cys) (0.977) and CKD-EPI(cr-cys) (0.908).
• In validation, CKD-EPI(cys), Eq(cys), and Eq(cys+nonrenal) showed similar bias and accuracy, with CKD-EPI(cys) demonstrating better precision than Eq(cys).
• Modified CKD-EPI(cr-cys) (0.908 × CKD-EPI(cr-cys)) and a combined equation (Eq(average)) showed comparable bias, accuracy, and precision.

Conclusions:

• The CKD-EPI(cys) equation performed well in the Japanese population, suggesting potential for cross-racial applicability without modification.
• Incorporating factors for extrarenal elimination of cystatin C might enhance the performance of GFR estimation equations.
• Limitations include a small number of participants with measured GFR >90 mL/min/1.73 m(2) and unmeasured extrarenal elimination of cystatin C.