Diabetes mellitus (DM) is increasingly prevalent worldwide and is a major risk factor for kidney impairment. Early identification of diabetic kidney disease (DKD) is crucial to prevent progression to end‑stage renal disease. This study evaluated the diagnostic performance of serum cystatin C in the early detection of DKD and compared cystatin C–derived estimated glomerular filtration rate (eGFR) with creatinine-based eGFR (MDRD equation).A cross‑sectional analytical study was conducted among 300 participants: 200 individuals with DM (subdivided into those with and without proteinuria) and 100 non-diabetic controls. Clinical history and physical examination were performed. Venous blood samples were analysed for serum creatinine, serum albumin, serum cystatin C, serum urea, and fasting blood glucose (FBG). Urine samples were collected to quantify urine albumin excretion. Median ages were similar across groups: 62.5 years in DM with proteinuria, 60.0 years in DM without proteinuria, and 60.0 years in controls (F = 3.524, p = 0.172). Compared with controls, diabetic participants had significantly higher FBG (141.0, 130.0 vs. 104 mg/dl; F = 68.456, p < 0.001), serum creatinine (109.0, 88.5 vs. 105.0 µmol/L; F = 35.50, p < 0.001), serum cystatin C (1.24, 1.11 vs. 0.84 mg/L; F = 59.27, p < 0.001), and urine albumin excretion (230.0, 102.0 vs. 30.0 mg; F = 128.62, p < 0.001).Among diabetics without proteinuria, reduced kidney function, defined by eGFR < 60 ml/min/1.73 m², was detected in 13% using the creatinine-based MDRD eGFR and in 23% using the cystatin C eGFR. Receiver operating characteristic (ROC) analysis showed that the AUC of cystatin C eGFR exceeded that of creatinine eGFR between urine albumin excretion levels of 30–300 mg. Cystatin C eGFR also demonstrated a stronger negative correlation with urine albumin excretion. Overall, cystatin C–derived eGFR was more sensitive than creatinine-based eGFR for early detection of DKD in people with DM.

Ndubuisi is a Specialist Registrar in Nephrology and Acute Medicine in the United Kingdom. His clinical work focuses on the management of acute medical conditions, with a particular interest in electrolyte disorders and diabetic emergencies. He has a growing academic interest in renal and metabolic medicine, including prior research on diabetic nephropathy. He is currently conducting an audit of hyponatraemia referral pathways to improve clinical decision-making and patient outcomes. Ndubuisi is committed to advancing his career in nephrology, with ongoing goals including completing the MRCP, making further research contributions, and actively engaging in medical education and quality improvement initiatives.