New Biomarker Allows Earlier Diagnosis of Kidney Disease

There is a growing body of evidence suggesting that Cystatin C can be used to detect kidney disease at earlier stages than serum creatinine. This may help facilitate prevention efforts in the elderly and those with diabetes, hypertension, or cardiovascular disease.

Cystatin C is a small, 13-kDa protein that is produced by virtually all nucleated cells. Its production rate is constant and is unaffected by inflammatory process, gender, age, and muscle mass. In the normal kidney, cystatin C is freely filtered at the glomerular membrane, and then nearly completely reabsorbed and degraded by the proximal tubular cells. Therefore, the plasma concentration of cystatin C is almost exclusively determined by the glomerular filtration rate (GFR), making it an excellent indicator of GFR.

A cystatin C assay kit developed by Diazyme (La Jolla, CA, USA) for the quantitative determination of Cystatin C in serum and plasma samples has been granted 510(k) clearance by the U.S. Food and Drug Administration (FDA; Rockville, MD, USA).

The Diazyme method is a liquid-stable, two-reagent system, which can be applied to most common clinical chemistry instrumentation. The cystatin C assay is based on a latex- enhanced immunoturbidimetric assay. Cystatin C in the sample binds to anti-cystatin C antibody, which is coated on latex particles, and causes agglutination. The degree of the turbidity caused by agglutination can be measured optically and is proportional to the amount of cystatin C in the sample.

The assay is precise and accurate, and offers an extended reportable range of 0.47 to over 8 mg/l, which will reduce the need for retesting elevated patient samples. The method also demonstrates insignificant bias from interfering substances commonly found in serum including highly elevated levels of hemoglobin, bilirubin, triglycerides, and ascorbic acid.

Diazyme is a company that has developed an extensive listing of instrument parameters and, along with multiple packaging formats, offers the added convenience of instrument-specific formats suitable for use in laboratories of all volumes and workflows. Diazyme Laboratories, a division of General Atomics, uses its platform technologies to develop low cost and uniform diagnostic products for clinical and research use. Products include diagnostic blood tests for liver disease, cardiac markers, diabetes, renal disease, and electrolytes.


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Diazyme
U.S. Food and Drug Administration