Cystatin C-based glomerular filtration rate estimating equations in early chronic kidney disease

Abstract

Objective: To compare performance of combined creatinine and cystatin C-based equation with equations based on either cystatin C or creatinine alone, in early chronic kidney disease.

Design: Diagnostic accuracy study.

Setting: Tertiary-care hospital.

Patients: One hundred children with chronic kidney disease who underwent 99mTc diethylenetriamine pentaacetic acid (DTPA) glomerular filtration rate measurement.

Methods: Estimating equations for glomerular filtration rate (GFR) based on serum cystatin C alone and in combination with serum creatinine were generated using regression analyses. These equations and the creatinine-based equation [0.42 x height/creatinine] were validated in 42 children with glomerular filtration rate between 60 and 90 mL/min/1.73 m2. Bias, precision and accuracy of estimating equations using DTPA glomerular filtration rate as gold standard.

Results: Cystatin C-based equation (GFR=96.9 - 30.4 x cystatin) overestimated while the combined cystatin C-and creatinine-based equation [GFR=11.45 x (height/creatinine) 0.356 x (1/cystatin) 0.188] underestimated the measured GFR. Cystatin C-based equation had less bias (1.9 vs. 12.4 ml/min/1.73 m2), and higher precision (13.1 vs. 25.6 mL/min/1.73 m2) and accuracy (92.1% vs. 75.7%) than creatinine-based equation. The combined cystatin C and creatinine equation had bias (-1.4 mL/min/1.73 m2) precision (15.2 mL/min/1.73 m2) and accuracy (91.2%) similar to cystatin C-based equation.

Conclusions: Cystatin C-based equation has a better performance in estimating glomerular filtration rate than creatinine-based equation in children with early chronic kidney disease. Addition of creatinine equation does not improve the performance of the cystatin C-based equation.