Frequency and clinical and transfusional significance of rheumatoid factor in patients with haemophilia and von Willebrand's disease.

Using a solid-phase radioimmunoassay for IgM rheumatoid factor, increased levels were found in 24% or 82 patients with haemophilia A, in 4 of 11 patients with haemophilia B, in 2 of 11 patients with haemophilia A with inhibitors and in 4 of 12 with von Willebrand's disease. The levels of rheumatoid factor increased significantly (p less than 0.02) after factor VIII concentrate or cryoprecipitate transfusions. No clinical or transfusional side effects could be attributed in these patients in relation to the presence of rheumatoid factor.