Cystatin C

Cystatin C is a protein that is produced by all body cells and serves as a marker for kidney function. The laboratory value measures the concentration of cystatin C in the blood and provides a more accurate assessment of the glomerular filtration rate (GFR) than serum creatinine.

A Cystatin-C test is recommended for: • People with suspected kidney diseases or impaired kidney function • Patients with diabetes, high blood pressure or other risk factors for chronic kidney diseases • Older people, as kidney function decreases with age • Patients for whom creatinine values are unreliable (e.g. due to strongly fluctuating muscle mass)

The test serves for the early diagnosis and monitoring of kidney diseases. It is also used to calculate the GFR, especially in patients for whom creatinine is not informative.

An elevated cystatin-C level indicates reduced kidney function. Symptoms may include: • Swelling (edema) • Fatigue, nausea or loss of appetite • High blood pressure in chronic kidney disease A low value is generally unproblematic and indicates normal kidney function. What is the ideal time for testing? The test can be performed at any time of day and is independent of food intake. Repeated tests are often helpful in assessing kidney function.

Cystatin C is less susceptible to influences such as muscle mass or diet, which makes it a reliable marker for the GFR. • Combined tests with cystatin C and creatinine provide a more precise assessment of kidney function. • An increased concentration can also occur in thyroid diseases, which should be taken into account in the interpretation.

The testing can be carried out at any time of the day and is independent of food intake. Repeated tests are often helpful for the assessment of kidney function.