Cystatin C Test

Dr Hasan explains how the test Cystatin C helps in the early detection of kidney dysfunction

Cystatin-C is a low-molecular-weight protein that is produced throughout the body by all cells that contain a nucleus and is found in the blood. Cystatin C is freely filtered and metabolized at a constant rate in the kidneys.

The test cystatin C helps screens for and monitors kidney dysfunction in those who are suspected of having kidney disease. It proves beneficial in the early detection of kidney disease where other tests results may still be normal. It is especially useful in cases where people have liver cirrhosis, are very obese, are malnourished or have reduced muscle mass.

Note: Cystatin C is not a commonly used test to ascertain renal function in people with Diabetes, as there are other more commonly used and effective tests- Blood Urea, Serum Creatinine, Urine Protein and Urine for Microalbuminuria.

Diagnosis

Normal values lie between:

1 to 50 years: 0.55 – 1.15 mg/L

> 50 years: 0.63 – 1.4 mg/L

An abnormal reading is denoted by a high pitched or turbulent sound or an irregular flow may indicate the exact location where an artery is blocked or narrowed and the presence of varicose veins. It also identifies if the blood vessels that supply oxygen and nutrients to a fetus are abnormally increased or decreased.

Reduced kidney functioning leads to a decrease in the Glomerular filtration rate. This in turn leads to an increase in cystatin C and waste products in the blood.

Increased levels of cystatin C may also indicate an increased risk of heart disease, heart failure and stroke.

Note: Glomerular filtration rate (GFR) is a marker of kidney health as it is the rate at which fluid is filtered in the kidneys.

Reliability

Since it is produced at a constant rate unaffected by age, sex, race, diet or nutritional status its estimation is better suited than creatinine alone or creatinine clearance for the calculation of GFR which is currently being used in all cases of Type I and Type 2 Diabetes.

Cystatin-C serves as an important measure of renal function in diabetics which is the most important cause of systemic renal disease in both Type I and Type II as it is able to catch the renal failure at an earlier date than serum creatinine. It also serves as an important risk predictor in cases of acute coronary syndrome.

This test is recommended to every patient where a rapid determination of renal function is required to start timely therapy by the Endocrinologists, Nephrologists, Oncologists and Obstetricians.

Performing the test

No preparation is required for testing cystatin-C which can be done at anytime during the day.

Blood is drawn from a vein in the patient's arm and cystatin C can be measured.

Advantages

• Cystatin C is an early, sensitive marker for kidney disease as it facilitates a precise and accurate estimation of the Glomerular filtration rate, a key determinant of kidney health.
• Cystatin C testing has higher usability as its levels are not affected by age, sex, race, diet, muscle mass or nutritional status.
• Test results are easy to interpret.

Dr Imtiaz Hasan is the Director of Pathology at Chellaram Diabetes Clinic, Pune.