How is it used?
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 , 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 test results may still be normal and an affected person may have few, if any, symptoms.
Researchers are exploring other uses of Cystatin C, and the reasons for doctors ordering it may evolve over time. In addition to kidney dysfunction, it has been associated with an increased risk of cardiovascular disease and heart failure in older adults.
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When is it ordered?
Cystatin C is gaining acceptance as studies confirm and define its usefulness, especially as an early, sensitive marker for chronic
kidney disease. It may be ordered when a person has a known or suspected disease that affects or potentially affects kidney function and reduces the glomerular filtration rate (GFR). It may be ordered when a doctor is not satisfied with the results of other tests, such as a
creatinine,
estimated GFR, or
creatinine clearance, or when he wants to check for early kidney dysfunction, particularly in the elderly, and/or wants to monitor known impairment over time.
Researchers are hoping to learn more about Cystatin C as an indicator of risk of heart failure and death, especially in older patients. In this case, the test may prove useful at times when a patient is at an increased risk of heart problems. For example, the test may be ordered as part of preoperative screening, before prescribing certain medications, or before performing scans that use dyes.
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What does the test result mean?
An increased serum Cystatin C corresponds to a decreased GFR and hence to kidney dysfunction. Since Cystatin C is produced throughout the body at a constant rate and removed and broken down by the kidneys, it should remain at a steady level in the blood if the kidneys are working efficiently and the GFR is normal. Concentrations of Cystatin C are not affected by gender, age, or race and Cystatin C is not affected by most drugs (see below), infections, diet, or inflammation.
Recent studies suggest that increased levels of Cystatin C may also indicate an increased risk of heart disease, heart failure, stroke, and mortality.
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Is there anything else I should know?
Cystatin C has been associated with hyperhomocysteinemia, which is often found in renal transplant patients, and it has been shown to increase with the progression of
liver disease. At least one study has looked at comparing Cystatin C levels in
serum with that found in
pleural effusion to help determine the cause of the effusion. These associations may or may not prove clinically useful.
Corticosteroids can increase levels Cystatin C levels while cyclosporine can decrease them. In the absence of kidney disease, Cystatin C levels may be elevated in rheumatic diseases and in malignant diseases, although they are not affected by tumor burden, the amount of cancer that someone has.
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