Radioimmunoassay of factor V in human plasma and platelets

Abstract

Homogeneous, single-chain human factor V was used to develop a double antibody competition radioimmunoassay to measure factor V concentrations in plasma and platelets. Standard curves were constructed that allow for the detection of as little as 20 ng factor V/ml of plasma. Normal factor V concentrations range from 4 to 14 micrograms/ml of plasma with an average value of 7.0 +/- 2.0 micrograms/ml (n = 64). No correlation was observed between antigen levels and age or sex. The radioimmunoassay data are consistent with factor V clotting assays, providing freshly drawn plasma is used in the bioassay. Radioimmunoassay of washed platelets indicate that 0.63–1.93 microgram of factor V is present per 2.5 X 10(8) platelets (4612–14128 molecules of the factor V platelet). When normalized to individual hematocrits and platelet count, the data indicated that platelets contribute approximately 18%-25% of the factor V found in whole blood. In addition, two individuals with functionally deficient factor V were examined and found to be deficient in both antigen and activity.

Clinical Phenotype and Genetic Analysis of Twins With Congenital Coagulation Factor V Deficiency

“…The factor Va level is ∼20 nM. [13][14][15] Factor Va acts as a cofactor during coagulation to substantially improve the catalytic efficiency of large enzyme complexes, thereby playing an important role in the rapid formation of thrombin. Congenital FVD is usually related to FV gene defects that lead to loss of function of FV.…”

“…The amino acid sequence of the light chain is partially homologous to the carboxyl terminal sequence of human factor VIII. The factor Va level is ∼20 nM 13–15. Factor Va acts as a cofactor during coagulation to substantially improve the catalytic efficiency of large enzyme complexes, thereby playing an important role in the rapid formation of thrombin.…”