Cystatin C

Does this test have other names?

No.

What is this test?

This test measures the amount of a protein called cystatin C in your blood.

Your body makes cystatin C constantly, and the protein is found in different fluids, including blood, spinal fluid, and breast milk. When your kidneys are healthy, they filter cystatin C out of the blood so it can be excreted in your urine.

This is a fairly sensitive blood test to look at your kidney health. Cystatin C can be used to calculate your glomerular filtration rate (GFR). Your healthcare provider can use this to see how well your kidneys are working and if there is a problem. It can also be used to check the progress of your disease, if you have kidney problems.

Why do I need this test?

You may need this test if your healthcare provider suspects that you have kidney problems.

You may also need this test if you are an older adult and your provider wants to find out your risk for heart complications. But this type of testing is not yet routinely done.

What other tests might I have along with this test?

Your healthcare provider may also order other tests to find out how well your kidneys filter toxins out of your blood. One of these tests is blood creatinine level.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

If you have an abnormally high concentration of cystatin C in your blood, it may mean you may have a kidney condition, such as chronic kidney disease.

Higher levels of cystatin C may also be caused by diabetes, cancer, HIV, hyperthyroidism, or hypothyroidism.

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

What might affect my test results?

Using steroids can affect your results.

How do I get ready for this test?

You don’t need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don’t need a prescription and any illegal drugs you may use.