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 filtration rate (GFR). We describe a fully automated and rapid particle-enhanced nephelometric immunoassay (PENIA) for measuring serum cystatin C on the Behring nephelometer systems (BNA, BN II). Each sample is analyzed 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%, respectively. There is absolute linearity across the assay range (r2 = 0.997), with analytical recovery by cystatin C addition between 95% and 109% (mean 102%). Hemoglobin (< or = 8.0 g/L), bilirubin (< or = 488 microL), triglycerides (< or = 23 mmol/L), rheumatoid factor (< or = 2000 kIU/L), and myeloma paraprotein (< or = 41 g/L) do not interfere with the assay. This assay agreed well with an in-house particle-enhanced turbidimetric immunoassay (PETIA) (mean difference = 1.73 +/- 2.10) and 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 of GFR estimation.