Testing & Self-Assessment
Creatinine
A key blood marker of kidney function
What it is
Creatinine is a waste product from normal muscle activity that the kidneys filter out of the blood. Blood creatinine levels are one of the most common lab values used to assess kidney function, and are the basis for most eGFR calculations.
How it's used
Rising creatinine levels over time can indicate declining kidney function. As with eGFR, trends across repeated tests are generally more informative than a single measurement.
Limitations
Creatinine levels are influenced by muscle mass, diet (including meat intake), hydration, and certain medications, which is part of why cystatin C is sometimes used as a complementary marker.