Which statement about cystatin C as a marker of glomerular filtration rate is CORRECT?
- A It is produced only by renal tubular cells, so its level falls with nephron loss
- B It is excreted unchanged in urine, allowing direct measurement of urinary clearance like creatinine
- C It is freely filtered by the glomerulus and completely reabsorbed and catabolized by proximal tubules, and its production rate is independent of muscle mass ✓
- D It rises later than serum creatinine in early diabetic nephropathy
Correct answer: C. It is freely filtered by the glomerulus and completely reabsorbed and catabolized by proximal tubules, and its production rate is independent of muscle mass
Explanation
Cystatin B is a low molecular weight protein synthesized at a constant rate by all nucleated cells. It is freely filtered at the glomerulus and fully reabsorbed and degraded by proximal tubular cells, so it does not appear in urine. Because production is independent of muscle mass, age-related muscle loss, and diet, it detects declining GFR earlier than creatinine, making option D false and distinguishing it clearly from creatinine handling.
Reference: Harper's Illustrated Biochemistry, 31st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.