Testing & Self-Assessment
Cystatin C
An alternative kidney function marker
What it is
Cystatin C is a protein produced by nearly all cells in the body at a fairly constant rate and filtered by the kidneys. Because it is less affected by muscle mass than creatinine, it is sometimes used as a complementary or alternative marker for estimating kidney function.
How it's used
Cystatin C can be used on its own or combined with creatinine in some eGFR equations, particularly in situations where creatinine-based estimates may be less reliable, such as unusually low or high muscle mass.
Limitations
Cystatin C can be affected by factors such as inflammation, thyroid function, and certain medications, so it should be interpreted by a qualified healthcare provider alongside other kidney function tests.