Cystatin C Test

What is the cystatin C test?

Cystatin C is a specific single-chain protein that is found in body fluids and is largely used as a biomarker for the functioning of the kidneys. It is also in focus for its role in predicting cardiovascular diseases and brain diseases including Alzheimer’s disease. The protein is filtered out of the blood by the tiny blood vessels called glomeruli in the kidneys.

These vessels allow water, various dissolved substances and wastes to pass through their walls but retain blood cells and larger proteins. While cystatin C and other substances are reabsorbed by the kidneys, other elements are excreted from the body. The reabsorbed cystatin C is not returned to the blood and is broken down by the proximal tubular cells. The rate of filtration of the fluids in the kidneys is called the glomerular filtration rate (GFR).

The test is used to measure the levels of cystatin C in the blood. Any problem in the kidneys results in a decline in the GFR rate and the increase in the levels of cystatin C and other measures of kidney function, such as creatinine and urea in the blood.

At the same time, effective kidney function can increase the GFF rates resulting in reduced amounts of cystatin C, creatinine and urea in the blood. Previously, the doctors used the blood levels of creatinine, a breakdown product that is produced by muscles, for measuring kidney function.

Due to the fact that creatinine levels are affected by diets and change in muscle mass, that test is presently considered unreliable. The cystatin C test is being considered more reliable as it is mostly unaffected by the muscle mass of the patient. This also makes it less influenced by other factors like sex, age, race, and diet.

The test is used for diagnosing chronic kidney disease (CKD) which is a common and serious complication of diabetes.CKD is a significant public health problem across the world and has an estimated prevalence of 13% in the western world.

It can progressively lead to kidney failure and also to other cardiovascular diseases. An accurate estimation of glomerular filtration rate (GFR) is essential for the diagnosis and management of CKD and the test is an important step in that aspect. Cystatin C is also a reliable marker of GFR rate for patient groups involving children, the elderly and patients with reduced muscle mass.

The detection of CKD at the preliminary stages of the disease is important for overall treatment and improving the survival and quality of life. Cystatin C is more effective in detecting earlier stages of renal dysfunction making it clinically more significant. On the other hand, creatinine levels in blood rise above the normal range when approximately 50% of renal function is already lost.

The serum cystatin C levels also have better diagnostic accuracy in determining the kidney functionality of patients with type 2 diabetes. The protein is also associated with increased risk of mortality, cardiovascular disease and heart failure in older adults. But these statements and the associated mechanisms are still being validated through tests before they are introduced in standard clinical practices.

Why do I need to undergo a cystatin C test?

The doctor can order the cystatin test under the following conditions.

In case a previous test for kidney function was inconclusive or needs to be confirmed, the healthcare provider may prescribe a cystatin C test to confirm whether or not you have kidney disease.

In case a patient has a suspected disease that affects kidney function and reduces the rate at which the kidneys filter impurities from the blood which is termed as the glomerular filtration rate.

It is used to determine the kidney functionality of patients who have liver cirrhosis, obesity-related problems, malnourishment, practice a vegetarian diet, have amputated limbs or very low muscle mass.

Since the levels of cystatin C change more rapidly, the test is used to diagnose the kidney functions of critically ill hospitalized patients.

How is a cystatin C test performed?

For cystatin C testing, a blood sample is collected from a vein through a needle and the process is termed as venipuncture. The entire process very simple and it involves the following steps.

– The collection area is disinfected by an antiseptic to prevent any infections. The collection site is generally around the elbow region but at times it can also be at the back of the hand.

– An elastic band is tied in the upper arm to make the vein swell with blood, thus making them more visible and the collection process easier.

– A needle is inserted into the vein and the required volume of blood is drawn through it in an attached vial. A slight stinging or pricking sensation is felt when the needle is inserted.

– The band is loosened to release the pressure on the arm and then the needle is withdrawn. Some pressure is applied on the site through a gauze or a cotton role to prevent any excess bleeding. The spot is then covered with a sterile bandage and the sample is sent to the laboratory for testing.

– The process is very safe and there is hardly any chance of complications. Since the size of the veins can differ from one person to the other, multiple punctures may be needed for some patients before the right vein is found. Some individuals might feel dizzy or lightheaded after the blood collection and may need the right level of care.

– Any pain or bruising in and around the collection site is generally cured within a few days. Chances of infection or excessive bleeding from the site are rare but in case of any such event, specific treatment might be needed. For infants or young children, veins are difficult to find and hence, a sharp tool called a lancet is often used to break the skin and collect the required volume of blood.

What is the price for cystatin C test? 

The cost of the test ranges between Rs 700 to Rs 2000 depending on the location and the specific facilities provided in the testing center.

When will I get the test results?

The test results are generally delivered within 24 to 72 hours depending on the laboratory.

What is the normal range for the cystatin C test?

The normal and healthy levels of cystatin C are considered between 0.57 – 1.05 mg/l. The results of the tests can vary slightly from one laboratory to another. Since the results depend on various factors including the clinical history of the patient, it is best interpreted by a physician.

What do the results mean?

Higher levels of the protein in the blood indicate a decreased glomerular filtration rate and point to kidney dysfunction. The levels should remain steady in the blood in case the kidney function is normal. In some cases, the higher levels of cystatin C can also be caused by ailments like diabetes, cancer, HIV, hyperthyroidism or hypothyroidism.

High concentrations of cystatin C are also associated with older age, an extension of coronary heart disease, CRP concentrations, and angiotensin-converting enzyme inhibitor and diuretic therapy. In many cases, an abnormal test result may not necessarily mean that you have a problem and the doctor can interpret the result in the best possible manner.

Do I need to fast for the cystatin C test?

One does not need to fast for undergoing this blood test.

What else do I need to know before I appear for a cystatin C test?

The following points can be kept in mind while appearing for the test.

It is best to inform the doctor about any drugs or medicines that you may be consuming including steroids, as these may affect the results.

Cystatin C can only be measured from a blood test and unlike creatinine, it is not found at detectable levels in the urine.

The levels of the protein can fluctuate in patients who have undergone kidney transplants.

The test may be associated with other tests including a simple urine test called ACR. This checks the level of protein in the urine for determining the effective filtrating ability of the kidneys.

Can pregnant women undergo a cystatin C test?

Pregnant women can undergo the test without any restrictions.

Is the cystatin C test possible for new-born babies?

The test is possible for new-born babies as per the doctor’s advice.