Creatinine clearance is used to estimate which renal parameter?

• A. Tubular secretion of creatinine
• B. Glomerular secretion of creatinine
• C. Renal glomerular and tubular mass
• D. Glomerular filtration rate

Answer: (D)

The key idea is that a substance whose clearance matches the rate of filtration by the glomeruli serves as an estimate of how well the kidneys are filtering, i.e., the glomerular filtration rate. Creatinine is produced at a fairly constant rate, is freely filtered at the glomerulus, and is not reabsorbed to any significant extent; only a small amount is secreted by the proximal tubules. Because of this near-filtration-only behavior, the clearance of creatinine closely tracks GFR, making it a practical estimate of how much plasma is being filtered by the kidneys each minute.

That’s why the correct choice is glomerular filtration rate. The other options don’t fit this concept: creatinine clearance isn’t a direct measure of tubular secretion, nor of a combined tubular–glomerular mass, and there isn’t a standard parameter called renal glomerular and tubular mass.