Which test is commonly used to assess kidney function?

• A. GFR
• B. Creatinine
• C. AST
• D. ALT

Answer: (B)

Kidney function is best understood through the glomerular filtration rate, which measures how much blood the kidneys can filter per minute. In practice, we don’t usually measure GFR directly; we estimate it from a blood test that measures serum creatinine and then adjust for factors like age, sex, and sometimes race. This estimated GFR, or eGFR, is the standard way clinicians gauge kidney function, track changes over time, and stage kidney disease.

Creatinine is a helpful marker because it is a waste product cleared by the kidneys, but by itself it isn’t a direct measure of filtration—its level can be influenced by muscle mass, diet, and other factors, so we rely on the calculated eGFR for a clearer picture of kidney function. AST and ALT are liver enzymes and don’t assess how well the kidneys are filtering. So the test most commonly used to assess kidney function is the GFR, typically estimated as eGFR from the creatinine level.