Detection of vitamin K deficiency by use of an enzyme-linked immunosorbent assay for circulating abnormal prothrombin.

A monoclonal antibody was raised against an abnormal decarboxylated prothrombin by a cell fusion technique. A cell line which produces an IgG1 murine antibody to the abnormal prothrombin, but not to prothrombin, was selected. Using this antibody we developed an enzyme-linked sandwich immunoassay for the abnormal prothrombin. The detection range was 0.5 X 10(-1) approximately 0.5 X 10(-3) micrograms protein of decarboxylated prothrombin and 0.5 approximately 0.5 X 10(-2) micrograms protein of abnormal prothrombin in vitamin K-deficient subjects. This discrepancy is attributable to a heterogeneity of decarboxylated prothrombin, depending on the number of gamma-carboxyglutamic acid residues. The antibody obtained had a higher affinity to a protein possessing less gamma-carboxyglutamic acid residues. The assay system developed may be useful for the detection of vitamin K deficiency, since a severe deficiency may result in less gamma-carboxyglutamic acid residues in the protein.