CYSTATIN C

Cystatin C

What it is

The Cystatin C test measures the level of cystatin C, a small protein produced by all nucleated cells in the body and filtered from the blood by the kidneys. Unlike creatinine, its level is less affected by muscle mass, age, or diet, making it a more sensitive and reliable marker of kidney function in many cases. It is often used to calculate estimated glomerular filtration rate (eGFR).

Uses

This test is primarily used to evaluate kidney function and detect early stages of chronic kidney disease (CKD). It is particularly useful in patients where creatinine-based tests may be less accurate, such as in the elderly, children, people with very low or high muscle mass, or those with certain chronic illnesses. Cystatin C may also be used to refine cardiovascular risk assessment.

Symptoms That May Lead to the Test

Your doctor may recommend a cystatin C test if you show signs of kidney dysfunction, such as swelling in the legs, fatigue, high blood pressure, changes in urination, or abnormal creatinine results. It may also be ordered for high-risk patients, such as those with diabetes, hypertension, or heart disease, to detect subtle declines in kidney function earlier.

Abnormal Results

High Cystatin C Levels: Indicate reduced kidney function and may suggest chronic kidney disease or acute kidney injury. Elevated levels may also correlate with increased cardiovascular risk.

Normal or Low Cystatin C Levels: Suggest healthy kidney function. A normal result helps rule out significant kidney disease when other findings are inconclusive.

Risks

The test involves a standard blood draw. Risks are minimal, including slight pain, bruising, or dizziness at the puncture site. These are temporary and usually resolve quickly.