Creatinine clearance (CrCl) consistently underestimates true GFR in which clinical scenario, making cystatin C a superior GFR marker?

• A Patients with massive obesity
• B Patients with uncontrolled diabetes mellitus
• C Patients with reduced muscle mass (cirrhosis, malnutrition, elderly) ✓
• D Patients on ACE inhibitors causing glomerular dilation

Explanation

Creatinine is generated from creatine in muscle; in conditions of severely reduced muscle mass (liver cirrhosis, malnutrition, cachexia, elderly), serum creatinine is disproportionately low relative to true GFR, causing CrCl to overestimate GFR. Conversely, in advanced muscle wasting, a 'normal' serum creatinine may mask significant renal impairment. Cystatin C is produced at a constant rate by all nucleated cells independent of muscle mass, making it a superior GFR marker in these contexts. Obesity increases creatinine generation, and ACE inhibitors reduce efferent arteriolar tone (not dilate glomeruli).

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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