Cystatin C (Serum or Plasma, Protein-Based Kidney Function Test)

What Is Cystatin C?

Cystatin C is a small protein produced by all cells in your body. Unlike traditional kidney function tests like creatinine, cystatin C levels are less affected by muscle mass or other factors. It’s often used alongside other tests to better evaluate kidney health.

How Is It Different from Other Kidney Tests?

Unlike creatinine, which can vary based on muscle size or diet, cystatin C levels are more consistent. It’s sometimes used in combination with creatinine to get a clearer picture of kidney function, especially in people with mild kidney issues or those who have high muscle mass.

Why Might Your Doctor Order This Test?

Your doctor may recommend a cystatin C test if you have symptoms of kidney problems (like fatigue, swelling, or frequent urination), if you have a condition that affects kidney function (like diabetes or high blood pressure), or as part of a routine checkup to monitor kidney health over time.

What Does the Test Involve?

A small blood sample is taken from your arm. The sample is sent to a lab where it’s analyzed to measure cystatin C levels. The result helps determine how well your kidneys are filtering waste from your blood.