Cystatin C: A serum protein that is filtered out of the blood by the kidneys and that serves as a measure of kidney function. Cystatin C is produced steadily by all types of nucleated cells in the body. Its low molecular mass allows it to be freely filtered by the glomerular membrane in the kidney. Its concentration in blood correlates with the glomerular filtration rate. The levels of cystatin C are independent of weight and height, muscle mass, age (over a year of age), and sex. Measurements can be made and interpreted from a single random sample. Cystatin C is a better marker of the glomerular filtration rate and hence of kidney function than creatinine, which is the most commonly used measure of kidney function.
The blood level of cystatin C predicts survival after one type of heart attack. A high level of cystatin C level in the blood after a heart attack is an ominous sign because it reflects the failure of the kidney to clear cystatin C from the blood into the urine.
A mutation of the cystatin C gene is responsible for a type of amyloidosis in which deposits in the brain result in premature strokes, intracranial hemorrhage, and dementia. This disease is called amyloidosis VI or cerebroarterial amyloidosis. It is inherited in an autosomal dominant manner.
Cystatin C has nothing to do with the statin drugs that are used to lower cholesterol. Cystatin C is also known as cystatin 3 and CST3.