INTRODUCTION:Chronic kidney disease (CKD) is a major public health concern, and for the assessment of patients with CKD, estimation of the glomerular filtration rate (GFR) is vital. Serum biomarkers, such as serum creatinine and serum cystatin C, have been commonly used to test renal function in patients who have chronic kidney disease (CKD). It is necessary to recognise the elevated risk of CKD progression to delay the deterioration of kidney failure and to plan for the evolution to end-stage renal disease. Therefore, the purpose of this study is to compare serum cystatin C and creatinine diagnostic output with measured GFR and estimated GFR in patients with CKD. METHODS:This study was conducted at SMHRC, Maharashtra India throughout the period of September 2019 to August 2020. We enrolled 100patients (50 males and 50 females) aged 40-60years with CKD stages2–5from Nagpur. In each patient, serum creatinine and serum cystatin C were determined. Serum cystatin C was measured with a particle-enhanced nephelometric immunoassay (PENIA) method. The detection methods for SCr were the enzymatic method and the Jaffe’s method. GFR was measured using diethylenetriaminepenta aceticacid (DTPA) renal scan method. Results: In females, serum cystatin C had significantly greater diagnostic specificity than serum creatinine. In males, no distinction between serum cystatin C and serum creatinine was observed. Serum cystatin C's diagnostic accuracy was significantly greater than that of creatinine. Conclusion: In young and elderly patients with CKD, serum cystatin C showed a high correlation with measured GFR compared with creatinine. Cystatin C is therefore a good alternative marker for CKD patients compared to creatinine. Our findings show that in patients with mild to moderately impaired kidney function, serum cystatin C is a reliable marker of GFR and has greater diagnostic accuracy than serum creatinine and measured clearance of creatinine.