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 (< or =30 mg/dl), triglycerides (< or =1000 mg/dl), intralipid (L index < or =1000), and rheumatoid factor (< or =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.