Performance characteristics of a cystatin C immunoassay with avian antibodies

Abstract

Background: A new particle-enhanced turbidimetric immunoassay (PETIA) with avian antibodies for measuring serum/plasma cystatin C has been developed. The performance characteristics of the assay are described. Methods: Measurements were performed on a Roche Modular P and on an Abbott Architect ci8200 using Gentian cystatin C immunoassay. Results: Measuring range was 0.3-8.0 mg/L. Reference range was 0.57-1.09 mg/L. Total analysis time was 10 minutes. Linearity was absolute over the whole assay range. Recovery of samples and controls was within 98.6-109.4%. Total imprecision CV, measured over 20 days with two lots, was ≤4.2%. Comparison with a particle enhanced nephelometric cystatin C immunoassay (PENIA) by linear regression resulted in a slope within 0.97-1.02 and intercept within ±0.05 mg/L. Interference studies with drugs, anticoagulants, intralipid (≤11g/L), triglycerides (≤14 g/L) and bilirubin (≤420 mg/L) showed no significant interference. Due to the use of avian antibodies, no interference with rheumatoid factor was observed. No carry-over was detected. Lower detection limit and lower quantification limit (CV ≤6%) were both below 0.33 mg/L, which is less than the lowest standard. Sample stability was up to one month at 2-8°C. Stability of the reagents at 2-8°C was estimated to be 24 months. Stability of the reagents in use was minimum 9 weeks. Conclusions: Gentian cystatin C PETIA is shown to have excellent performance characteristics. Correlation with existing PENIA shows no significant difference between methods. Interference results are improved due to avian antibodies and a broader span of the calibration curve. Avian antibodies are also known to have better immune response than mammalian antibodies towards mammalian antigens.