When should a creatinine clearance test be done instead of an eGFR test?

A creatinine clearance test may be preferred over an estimated glomerular filtration rate (eGFR) test in cases where muscle mass varies greatly, such as in bodybuilders or patients with muscle-wasting conditions. This is because the eGFR can sometimes give inaccurate results for individuals with unusual muscle mass. The creatinine clearance test provides a more accurate assessment of kidney function in these situations by directly measuring creatinine filtration over 24 hours.