Measurement of Antihaemophilic Factor A Antigen (VIII:CAg) with a Solid Phase Immunoradiometric Method Based on Homologous Non‐Haemophilic Antibodies

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Abstract
Antihaemophilic-factor-A-antibodies, which had spontaneously arisen in 2 patients, were used to develop an immunoradiometric method for measurement of antihaemophilic factor A antigen (VIII:CAg). 13 patients with severe haemophilia A had VIII:CAg below the limit of detection (0.01 U/ml). Patients with moderate and mild haemophilia A either had VIII:CAg roughly equal to factor VIII clotting activity (VIII:C) or a not detectable VIII:CAg, suggesting 2 different molecular mechanisms in moderate and mild haemophilia A. VIII:CAg could be detected in serum but in lower amounts than in plasma. In 2 patients with von Willebrand's disease VIII:CAg equalled VIII:C. The post-transfusional retarded increase of VIII:C in 1 patient with von Willebrand's disease was accompanied by a slight increase in VIII:CAg. Fetal plasma contained measurable amounts of VIII:CAg.