Quantitative Automated Particle-Enhanced Immunonephelometric Assay for the Routinary Measurement of Human Cystatin C
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Michele Mussap
Abstract
Human cystatin C is a low molecular mass protein of 13359 Dalton recently proposed as a new very sensitive marker of changes in glomerular filtration rate. Serum cystatin C concentration correlates negatively with glomerular filtration rate as well as or better than creatinine. We evaluated a recently introduced automated nephelometric immunoassay for cystatin C in serum or EDTA-plasma samples on the Behring Nephelometer System. The assay consists of incubating the 100-fold diluted sample for 6 minutes with latex particles covalently coated with anti-human cystatin C antibodies, and then quantifying the change of light-scatter produced. Method reproducibility is satisfactory, the intra-and inter-assay coefficients of variation ranging from 1.58 % to 3.77 % and from 5.6 % to 11.47 % respectively. Rheumatoid factor (≤ 1116 IU/ml), bilirubin (≤ 418 μmmol/l), triglycerides (10.47 mmol/l), and haemoglobin (12 g/l) do not significantly interfere in the assay. No significant difference was found in cystatin C concentration between serum and EDTA-plasma samples. Cystatin C is stable in serum samples stored under different conditions up to one month. This method correlates well (mean difference = −0.536 ± 0.307 mg/l) with another commercially available particle-enhanced turbidimetric immunoassay. Cystatin C offers better clinical sensitivity than creatinine for discriminating patients with normal renal function and those with mild-to-moderate reduction in renal function. This method is suitable for routine cystatin C measurement, including emergencies.
Walter de Gruyter GmbH & Co. KG
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