ELISA for determination of total coagulation factor XII concentration in human plasma.

Human blood coagulation factor XII (FXII) is the one chain 80 kDa zymogen form of the active serine protease α-FXIIa, which consists of a heavy and light chain linked by a disulfide bond, the light chain being responsible for the proteolytical activity. FXII is the first component of the contact dependent pathway of coagulation, but its physiological role is still subject to debate. In the present study we utilized two monoclonal antibodies against the heavy chain of FXII to establish a sandwich enzyme linked immunosorbent assay (ELISA) for quantification of total FXII concentration in human plasma samples. A unique characteristic of this assay is its equal recognition of FXII and inhibitor bound FXII. This is important, as inhibitor complexes of α-FXIIa are formed in vivo as well as during blood sampling and handling. Validation of the assay demonstrated a high sensitivity, with a limit of detection and quantification of 1.2 ng/mL and 2.6 ng/mL respectively. The coefficients of variation for the repeatability and within-laboratory standard deviations were 2.6% and 5.2% respectively. The reference interval determined from healthy volunteers (n=240) was 10.6-43 mg/L.