Performance evaluation of a particle-enhanced turbidimetric cystatin C assay on the Hitachi 917 analyzer

Background: Human cystatin C is a low molecular weight protein that has been proposed as a new endogenous marker of glomerular filtration rate. We investigated the performance of the Genzyme cystatin C assay on the Hitachi 917 analyzer. Methods: Imprecision. linearity. recovery, and interference studies were performed on the Hitachi 917 analyzer. For method comparison, split sample aliquots were assayed using the described method and 2 other commercially available cystatin C assays. Results: The assay was linear from 0.24 to 6.36 mg/l. Within-run coefficient of variation (CV) was 4.2 and 0.8% at cystatin C concentrations of 0.50 and 2.00 mg/l, respectively. Between-run CV was 4.3 and 2.7% at the same concentrations. The average analytical recovery was 99%. Bilirubin (<= 30 mg/dl), triglycerides (<= 1000 mg/dl), intralipid (L index <= 1000), and rheumatoid factor (<= 1000 IU/ml) did not interfere with the assay. A > 10% change in cystatin C level was observed when hemoglobin concentration was > 800 mg/dl. The assay compared well with the Dade Behring immunonephelometric assay and the Dako immunoturbidimetric assay. Conclusion: The Genzyme cystatin C immunoassay is an acceptable method for the determination of cystatin C on the Hitachi 917 analyzer. (C) 2008 Elsevier B.V. All rights reserved.