Evaluation of Cystatin C versus Creatinine for the Assessment of Glomerular Filtration Rate in Indian Patients with Type 2 Diabetes: An Eight-Week Prospective Study

Abstract

Background: Traditional creatinine-based estimated glomerular filtration rate (eGFRcr) is often inaccurate in populations with specific body compositions, such as the sarcopenic obesity phenotype common in India. This study aimed to quantify the discordance between creatinine and Cystatin C-based eGFR (eGFRcys) and its impact on Chronic Kidney Disease (CKD) staging.

Methods: In this prospective, eight-week observational cohort study, 62 patients with Type 2 Diabetes Mellitus were recruited from a tertiary hospital. Renal function was estimated using CKD-EPI 2021 (Creatinine) and CKD-EPI 2012 (Cystatin C) equations. The primary endpoint was the CKD stage re-classification rate. Secondary endpoints included the magnitude of the "eGFR gap" and its correlation with the Fibrosis-4 (FIB-4) index and BMI.

Results: The mean eGFRcr was significantly higher than the mean eGFRcys (76.4 ± 14.2 vs. 64.8 ± 11.5 mL/min/1.73m²; p < 0.001), with a mean eGFR gap of 11.6 ± 4.8 mL/min/1.73m². A total of 22 patients (35.5%) were re-classified to a more severe CKD stage using Cystatin C. The FIB-4 index (beta = 0.42, p < 0.01) and BMI (beta = -0.31, p = 0.02) were independent predictors of the eGFR gap. The discordance remained stable over the eight-week follow-up period (p = 0.42).

Conclusion: Relying solely on serum creatinine creates a significant "renal blind spot," masking early-stage kidney disease in over one-third of the studied cohort. Integrating Cystatin C into clinical protocols is essential for accurate renal staging and early nephroprotection in Indian diabetic patients.