Immunonephelometric determination of the C4B-binding protein

Abstract

A fully mechanised immunonephelometric method for the rapid and specific determination of C4b-binding protein (C4b-BP) in citrated plasma is described. The method utilizes commercially available rabbit antiserum against human C4b-BP and a nephelometer analyser. A single determination can be performed within 6 min, requiring 80 μl sample volume. The measuring range is about 10 to 200 % of normal C4b-BP. Precision is characterized by intraassay coefficients of variation between 1.5% and 2.8%, and interassay coefficients of variation between 4.0% and 4.6% for the same C4b-BP concentrations. The nephelometry of C4b-BP was correlated with electroimmunodiffusion (Laurell technique; r=0.863, y=0.909x+7.091, n=79). C4b-BP concentrations (143%, 96–223%; median and 2.5th-97.5th percentile) from 83 subjects with increased inflammation markers C-reactive protein (>10 mg/I), and fibrinogen (>4.5 g/I) showing significantly higher C4b-BP concentrations compared to 151 obviously healthy subjects (97%, 68–141%; p <0.001). In contrast to 81 patients with therapeutic heparinisation (90%, 60–131%) significant decreased concentrations were found in 90 subjects under oral anticoagulant therapy (OAT) in the stable state (78%, 44–125%; p <0.001). Depending on different INR levels (<2.5, n=40: 71%, 63–85%; >2.5, n=50: 81%, 68–92%; median and 25th-75th percentile) no significant differences of C4b-BP concentrations could be measured.