creatinine clearance have been widely replaced by many other tests like eGFR and Cystatin C
Cystatin C is a cysteine proteinase inhibitor, a small molecule that is produced by nucleated
cells. Serum Cystatin C is filtered out of the blood by the kidneys and that serves as a measure
of kidney function. Its low molecular mass allows it to be freely filtered by the glomerular
membrane in the kidney.
Since it is formed at a constant rate and freely filtered by the healthy kidney, cystatin C is a
good marker of renal function. Serum concentrations of cystatin C are almost totally
dependent on glomerular filtration rate (GFR). A reduction in GFR causes a rise in the
concentration of cystatin C. Cystatin C is a better marker of the glomerular filtration rate and
hence of kidney function than creatinine which was the most commonly used measure of kidney function
The levels of cystatin C are independent of weight and height, muscle mass, age (over a year
of age), sex, and factors which have been demonstrated to affect creatinine values. In
addition, a rise in creatinine does not become evident until the GFR has fallen by
approximately 50%. Measurements can be made and interpreted from a single random sample.
Cystatin C may be used as an alternative to creatinine and creatinine clearance to screen for
and monitor kidney dysfunction in those with known or suspected kidney diseases. It may be
especially useful in those cases where creatinine measurement is not appropriate: for instance
in those who have liver cirrhosis, are very obese, are malnourished or have a reduced muscle
mass. Measuring Cystatin C may also be useful in the early detection of kidney disease when
other parameters might still be normal, especially in the elderly.
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 been associated with hyperhomocysteinemia (often found in renal transplant
patients), and it has been shown to increase with the progression of liver disease
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
Serum or plasma
Red-top tube or green-top (heparin) tube
Refrigerate at 2°C to 8°C. Stable for 7 days. Stable when frozen for up to 3 months.
Overnight fasting is preferred.
Causes for Rejection
Specimen other than serum or heparinized plasma; gross lipemia that cannot be cleared by ultracentrifugation[/b]