Chronic kidney disease is a worldwide health problem that carries a substantial risk for cardiovascular morbidity and death. Current guidelines define chronic kidney disease as kidney damage or glomerular filtration rate (GFR) less than 60 mL/min per 1.73 m2 for 3 months or more, regardless of cause. GFR is the most frequently used criteria in the assessment of renal function.
Serum creatinine is the most commonly used marker for estimation of GFR. However, it has become evident that the creatinine concentration is far from ideal because it is significantly changed by other factors such as muscle mass, diet, gender, age and tubular secretion.
Cystatin C is produced by all nucleated cells at a constant rate and the production rate in humans is remarkably constant over the entire lifetime. Elimination from the circulation is almost entirely via glomerular filtration. For this reason the serum concentration of cystatin C is independent from muscle mass and gender. There is a small dependency of cystatin C concentration from age in the age range 1 to 50 years whereas the cystatin C concentration of healthy individuals > 50 years increases with age. Therefore, cystatin C in plasma and serum has been proposed as a more sensitive marker for GFR in children and adults, and several studies, as well as one meta analysis, have suggested that cystatin C is superior to serum creatinine for estimation of GFR. Patient groups which benefit most are those with mild to moderate kidney disease and also those in acute renal failure, where toxic drugs have to be administered which are excreted by glomerular filtration, especially elder people (> 50 years), children, pregnant women with suspicion of pre - eclampsia, diabetics, people with diseases of skeletal muscle and renal transplant recipients. Additionally cystatin C has been discussed in recent literature as a prognostic marker for acute heart failure.
As with creatinine several cystatin C based prediction equations for calculation of GFR for adults and children have been published. It should be noted that these formulas were evaluated with different cystatin C assays (particle - enhanced nephelometric immunoassay PENIA or particle enhanced turbidimetric immunoassay PETIA) and may reveal inaccurate GFR results if an inappropriate combination of formula and assay is used.
CKD-EPI cystatin C equation for estimating GFR:
Serum cystatin C ≤ 0.8 mg/L:
Male 133 × (Scys/0.8)−0.499 × 0.996Age
Female 133 × (Scys/0.8)−0.499 × 0.996Age × 0.932
Serum cystatin C > 0.8 mg/L:
Male 133 × (Scys/0.8)−1.328 × 0.996Age
Female 133 × (Scys/0.8)−1.328 × 0.996Age × 0.932
Cystatin C equation for estimating GFR acc. to Horio M et al.:
Male 96 × SCysC−1.324 × 0.996Age
Female 96 × SCysC−1.324 × 0.996Age × 0.894
Cystatin C equation for estimating GFR acc. to Grubb A et al.:
eGFR = 130 × Cystatin C−1.069 × Age−0.117 − 7
SI units Conversion Calculator. Convert Cystatin C level to mg/l, mg/dl, mg/100ml, mg%, µg/ml. Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Cystatin C unit conversion to mg/l, mg/dl, mg/100ml, mg%, µg/ml.