Performance and determinants of serum creatinine and cystatin C based glomerular filtration rate estimating equations in South Asians

Abstract Introduction Creatinine-based CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) estimated glomerular filtration rate equation (eGFR) was calibrated for the general Pakistan population (eGFRcr-PK) to eliminate bias and improve accuracy. Cystatin C-based CKD-EPI equations (eGFRcys and eGFRcr-cys) have not been assessed in this population, and non-GFR determinants of cystatin C are unknown. Methods We assessed eGFRcys and eGFRcr-cys, and non-GFR determinants of cystatin C in a cross-sectional study of 557 participants (≥40 years) from Pakistan. We compared bias (median difference in measured GFR [mGFR] and eGFR), precision (interquartile range of differences), accuracy (percentage of eGFR within 30% of mGFR), root mean square error (RMSE), and classification of mGFR Results We found that eGFRcys underestimated mGFR (bias: 12.7 ml/min/1.73 m2 [95% confidence interval: 10.7-15.2]). eGFRcr-cys did not improve performance over eGFRcr-PK in precision (P=0.52), accuracy (P=0.58), or RMSE (P=0.49). Results were consistent among subgroups by age, sex, smoking, body mass index (BMI), and eGFR. NRI was 7.31% (1.52%-13.1%; P Conclusion eGFRcys underestimated mGFR in South Asians and eGFRcr-cys did not offer substantial advantage compared to eGFRcr-PK. Future studies are warranted to better understand the large bias in eGFRcys and non-GFR determinants of cystatin C in South Asians.