INITIAL EVALUATION OF CYSTATIN-C MEASUREMENT BY PARTICLE-ENHANCED IMMUNONEPHELOMETRY ON THE BEHRING NEPHELOMETER SYSTEMS (BNA, BN-II)

Serum cystatin C has been suggested as a new marker of glomerular filt ration rate (GFR). We describe a fully automated and rapid particle-en hanced nephelometric immunoassay (PENIA) for measuring serum cystatin C on the Behring nephelometer systems (BNA, BN II). Each sample is ana lyzed in 6 min with as many as 75 samples per batch. The assay covers the range 0.23-7.25 mg/L, up to seven times the upper limit of normal. The intra- and interassay imprecision are <3.3% and <4.5%, respective ly. There is absolute linearity across the assay range (r(2) = 0.997), with analytical recovery by cystatin C addition between 95% and 109% (mean 102%). Hemoglobin (less than or equal to 8.0 ;g/L), bilirubin (l ess than or equal to 488 mu L), triglycerides (less than or equal to 2 3 mmol/L), rheumatoid factor (less than or equal to 2000 kIU/L), and m yeloma paraprotein (less than or equal to 41 g/L) do not interfere wit h the assay. This assay agreed well with an in-house particle-enhanced turbidimetric immunoassay (PETIA) (mean difference = 1.73 +/- 2.10) a nd a commercial PETIA (mean difference = 1.13 +/- 0.86). This is a new assay by which cystatin C may be effectively used as a marker ob: GFR estimation.