Comparison of Creatinine and Cystatin C-based Estimated Glomerular Filtration Rate in Relation to Glycemic Control Among Patients With Type 2 Diabetes Mellitus

Abstract

Background & Objectives: Diabetic kidney disease (DKD) is a major complication of type 2 diabetes mellitus (T2DM) leading to end-stage renal disease (ESRD). Early identification of declining renal function is vital to prevent disease progression. Estimated glomerular filtration rate (eGFR) calculated using serum creatinine or serum cystatin C serves as a key indicator of kidney function. This study aimed to compare creatinine-based (MDRD equation) and cystatin C-based (CKD-EPI 2012 equation) eGFR in relation to glycemic control (HbA1c) in patients with type 2 diabetes mellitus and healthy controls.
Materials & Methods: This cross-sectional case–control study included 150 participants aged 25–70 years, comprising 75 clinically diagnosed T2DM patients (cases) and 75 apparently healthy individuals (controls). Patients with hypertension, known chronic kidney disease, hepatic/muscular disorders, or those undergoing dialysis were excluded. Serum creatinine (enzymatic method) and serum cystatin C (immunoturbidimetric assay) were analyzed on a Beckman AU5800 clinical chemistry analyzer. Glycated hemoglobin (HbA1c) was measured by high-performance liquid chromatography (HPLC). eGFR was calculated using the MDRD equation for creatinine and the 2012 CKD-EPI equation for cystatin C. Statistical analyses included independent Student’s t-test, paired t-test, Pearson’s correlation, and Receiver Operating Characteristic (ROC) curve analysis.
Results: Mean HbA1c, serum creatinine, and serum cystatin C levels were significantly higher in T2DM cases than in healthy controls. Mean eGFR was significantly lower in diabetic patients compared to controls with both the MDRD equation (84.84 mL/min/1.73 m² vs. 98.07 mL/min/1.73 m²) and the CKD-EPI cystatin C equation (79.2 mL/min/1.73 m² vs. 90.35 mL/min/1.73 m²). A paired t-test demonstrated no statistically significant difference between eGFR calculated by MDRD and CKD-EPI (p = 0.318). Both eGFR estimates showed a significant inverse correlation with HbA1c (p < 0.05). ROC curve analysis showed excellent and comparable diagnostic performance for detecting early renal impairment (eGFR< 90 mL/min/1.73 m), with an area under the curve (AUC) of 0.95 (95% CI: 0.93–0.98) for creatinine-based eGFR and 0.96 (95% CI: 0.93–0.98) for cystatin C-based eGFR.
Conclusion: Both creatinine-based (MDRD) and cystatin C-based (CKD-EPI) eGFR equations provide comparable clinical performance in evaluating renal function in patients with type 2 diabetes mellitus. Poorer glycemic control correlates with declining GFR, highlighting the value of early eGFR assessment alongside glycemic monitoring to identify individuals at risk of diabetic kidney disease.