Evaluating the Diagnostic Utility of Cystatin C versus Creatinine in Chronic Kidney Disease: A Cross-Sectional Analysis.

BACKGROUND: Chronic kidney disease (CKD) is a progressive condition with high prevalence in India, often driven by diabetes and hypertension. Early detection is critical, yet serum creatinine, the conventional biomarker, is influenced by non-renal factors and lacks sensitivity in early stages. Cystatin C, a low molecular weight protein unaffected by muscle mass or diet, has emerged as a promising alternative. This study evaluates the diagnostic utility of serum cystatin C versus creatinine in detecting and monitoring CKD among Indian patients. METHODS: A cross-sectional observational study was conducted at Indira Gandhi Institute of Medical Sciences, Patna, over 18 months, enrolling 150 participants: 75 patients with CKD (grades 3-5) and 75 healthy controls. Serum cystatin C was measured using an enzyme-linked immunosorbent assay and serum creatinine via the kinetic Jaffe method. Estimated glomerular filtration rate (eGFR)Cr-Cys, eGFRCr, and eGFRCys were calculated using Chronic Kidney Disease Epidemiology Collaboration or CKD-EPI equations based on both biomarkers (serum creatinine and serum cystatin C). Statistical analyses were conducted using t-tests, chi-square tests, and Pearson correlation coefficients to compare biomarker levels and assess their relationship with eGFR. RESULTS: Both serum cystatin C and creatinine were significantly elevated in patients with CKD compared to controls (p<0.0001). Cystatin C showed a stronger negative correlation with eGFRCr-Cys (r = -0.91) than creatinine (r = -0.896). A high concordance (r = 0.90) was observed between eGFR values derived from cystatin C and creatinine equations in patients with CKD, particularly in diabetic subgroups and early-stage CKD. In healthy controls, this correlation was weaker and non-significant. CONCLUSION: Serum cystatin C is a sensitive and reliable biomarker for CKD detection, demonstrating superior correlation with eGFRCr-Cys compared to creatinine. Its diagnostic performance is especially valuable in early-stage disease and high-risk populations. Integrating cystatin C into routine clinical practice could enhance early diagnosis and improve patient outcomes, though cost and assay availability remain barriers.