Cystatin C is increasingly used as a marker of glomerular filtration rate (GFR) in preference to creatinine in certain clinical contexts. In which specific population is cystatin C most superior to creatinine-based GFR estimation?

• A Bodybuilders with high creatine phosphate stores
• B Patients on high-protein diets with elevated tubular secretion of creatinine
• C Patients with polycystic kidney disease where cysts clear cystatin
• D Elderly patients with sarcopenia and reduced muscle mass ✓

Explanation

Creatinine-based GFR estimation depends on steady-state creatinine production from muscle creatine phosphate metabolism. In elderly, cachectic, or sarcopenic patients with reduced muscle mass, serum creatinine is disproportionately low despite significantly impaired GFR, leading to overestimation of GFR. Cystatin C is produced at a constant rate by all nucleated cells and is independent of muscle mass, making it a superior GFR marker in sarcopenic individuals. In bodybuilders, creatinine would be elevated rather than falsely low.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.