Evaluation of the Dade Behring N Latex Cystatin C assay on the Dade Behring Nephelometer II system

The Dade Behring N Latex Cystatin C assay, a particle-enhanced nephelometric immunoassay for measuring serum cystatin C, was evaluated on the Dade Behring Nephelometer II. The assay time was 6 min and the throughput was 75 samples per hour. The sample volume was 40 mu L and the measuring range was 0.25 - 7.90 mg/L. Imprecision studies revealed within-run CVs <1.8% and between-run CVs <1.8% in the concentration range 0.87 - 4.63 mg/L. Recovery was 92.4 - 101.3%. Linearity studies showed excellent correlation between the theoretical and obtained values. No interferences were detected from haemoglobin <1.0 mmol/L, bilirubin <512 mu mol/L and Intralipid(R) <20 g/L. Stability of cystatin C in serum was 7 days at temperatures from 20 degrees C to - 20 degrees C and 6 months at - 80 degrees C. Measurements of cystatin C in heparin-plasma and EDTA-plasma did not differ significantly from cystatin C measured in serum. Fifty patient samples run on the Dade Behring Nephelometer II (y) were compared to the Dako Cystatin C assay (x). The Passing-Bablok regression analysis revealed y=1.105x - 0.340. In conclusion, the Dade Behring N Latex Cystatin C assay was precise and correlated with the Dako Cystatin C assay.