Serum creatinine vs. Cystatin C

Serum creatinine isn’t always the best indicator of a patient’s GFR, especially when muscle mass is a factor. Low muscle mass can lower creatinine levels, while high muscle mass can lead to higher levels.

For a more accurate assessment, consider ordering a cystatin C test. Unlike creatinine, cystatin C levels are not influenced by muscle mass. The kidneys freely filter it, and neither secrete nor reabsorb it in the renal tubules.

A cystatin C test can clarify whether a patient with low muscle mass might be understated based on creatinine or if a patient with high muscle mass might be incorrectly diagnosed with chronic kidney disease due to elevated creatinine.