A 48-year-old female patient has a GFR of 40 mL/min and a serum creatinine of 1.5 mg/dL. Which value best represents her creatinine clearance in mL/min?

• A. 46.85
• B. 35.13
• C. 39.82
• D. 23.15

Answer: (C)

Creatinine clearance is a practical estimate of how well the kidneys are filtering, essentially mirroring the glomerular filtration rate. Since creatinine is produced at a steady rate and is freely filtered (with a bit of secretion that can make CrCl slightly higher than the true GFR), CrCl generally tracks GFR closely.

Here, the patient has a GFR around 40 mL/min, reflecting moderately reduced kidney function. The creatinine clearance should be in that same ballpark. Among the numbers given, the one closest to 40 is 39.82 mL/min, which best represents her creatinine clearance. The tiny difference from 40 arises from measurement and individual variability, not a fundamental mismatch in the concept.