Which statement about creatinine clearance is true?

• A. It measures hepatic function
• B. It is unaffected by urine collection timing
• C. It estimates glomerular filtration rate
• D. It reflects urinary protein excretion

Answer: (C)

Creatinine clearance reflects how well the kidneys are filtering blood, which is why it provides an estimate of glomerular filtration rate. Creatinine is produced at a steady rate, freely filtered by the glomeruli, and not significantly reabsorbed; because of this, the amount cleared from the plasma per unit time largely mirrors the filtration capacity of the kidneys. The usual way to obtain this value is by comparing creatinine in urine with creatinine in blood over a collection period, often 24 hours, so the calculation approximates GFR. Some creatinine is secreted by the tubules, so clearance can slightly overestimate true GFR, but the overall concept remains: it’s an estimate of filtration, not a measure of liver function. It does not directly assess urinary protein excretion—that’s a separate measurement (proteinuria). The accuracy depends on proper urine collection timing; incomplete or inconsistent collection biases the result because it relies on the total urine output over the period.