Cystatin C

The Cystatin C test is not routinely used at the moment but it is likely to be used on a regular basis in the future; it may prove a useful alternative to the creatinine test to assess kidney function. Cystatin C is a protein, which is produced by nucleated cells in the body (these cells have genetic material in their centre); it is produced at a constant rate and is found in a variety of bodily fluids, including spinal fluid, breast milk and serum.

When is the test used?

The test is not widely available at the moment but it is believed it will be used regularly in the future when a doctor suspects that a patient has problems with their kidneys. The test may be preferable to the creatinine test because some patients, including those with low muscle mass, obese patients and those with liver disease, have problems with creatinine test.

The test will be ordered when the doctor suspects a patient has symptoms of poor kidney function or an illness, which may affect kidney function.

How is the test done?

The test is done by collecting and analysing a sample of blood from a vein in the arm; a needle in inserted into the vein and the blood is drawn into a syringe. Once the sample has been collected, it will be bottled, labelled with the patient’s name and sent away to the laboratory for evaluation.

What do the test results show?

If levels of Cystatin C are high, this indicates that the kidneys are not functioning as effectively as they should be. Elevated levels of Cystatin C in the serum indicate a low GFR (glomerular filtration rate). The levels of Cystatin C should remain constant if the GFR is normal and the kidneys are working properly.

Cystatin C levels may also be elevated when a patient has health conditions, including cancer and rheumatic conditions. Certain types of medication, including corticosteroids, may also affect Cystatin C levels.

Specific Blood Tests

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