Liquid Cystatin C Assay– a Good Indicator of GFR

As a more sensitive maker of renal dysfunction, cystatin C offers several advantages over traditional creatinine assays.

Cystatin C is unaffected by nonrenal factors including muscle mass, weight, height, age, gender, diet and drugs. Therefore it is particularly useful in cases where creatinine measurement is not appropriate e.g., in individuals who are obese, malnourished, or who have liver disease.

The Randox (Crumlin, United Kingdom) cystatin C assay is based on an immunoturbidimetric method and is suitable for use on a wide range of chemistry analyzers. All reagents are supplied liquid ready to use for added convenience; furthermore, reagents are stable for 28 days at +10 °C onboard the analyzer, minimizing the possibility of reagent waste.

The assay has a wide measuring range of 0.4 to 10 mg/L allowing both normal and abnormal values to be measured accurately and reliably without the need for additional dilutions. Further benefits include precision (CVs under 5%) and limited interference from bilirubin, hemoglobin, triglycerides, and intralipids. A full range of supporting quality controls and calibrators are also available.

Cystatin C is sensitive to changes in the “creatinine blind” range enabling detection of early reductions in GFR and subsequent early treatment of kidney disease. Cystatin C has several other advantages over creatinine; the ability of cystatin C to detect even small changes in GFR makes it the ideal marker for dosing medication eliminated by the kidneys. Cystatin C is also the preferred marker for estimating GFR in infants, the elderly, diabetics, and those with reduced muscle mass.

Traditionally creatinine was the most widely used marker of GFR and kidney function but several recent studies have documented cystatin C as a far superior and sensitive marker. Cystatin C is produced at a constant rate throughout the body and is removed and broken down by the kidneys, levels will therefore remain steady if the kidneys are working efficiently and the GFR is normal.

The prevalence of chronic kidney disease continues to increase dramatically as does the burden on healthcare resources. The early detection of kidney disease is crucial in order to lower healthcare costs, avoid disease progression, and reduce the need for dialysis or transplantation.

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