Anomalous reactions in the haemagglutination assay for anti-collagen antibodies: studies on patients with rheumatoid arthritis or chronic low back pain.

Sera from 23 patients with chronic low back pain, 20 rheumatoid patients and 16 normal controls were tested for antibodies to collagen types I, II and III, both native and denatured, by haemagglutination. Weak reactions against denatured collagen types I and II were found in 30-40% of the sera. Sera from individuals with rheumatoid arthritis or chronic low back pain behaved similarly, while only one normal serum showed any positive reaction. Reactions to denatured collagen type III and to native collagen of all 3 types were largely negative. Non-antibody serum components were thought to be responsible for these haemagglutination reactions since weakly positive reactions were abolished by cryoprecipitation and could not be confirmed by a solid-phase fluorimetric assay. Using the latter technique sera from 62 rheumatoid patients were screened for antibodies to type II collagen (native and denatured) and only one positive serum found. We conclude that haemagglutination is subject to false positive reactions and that the incidence of anticollagen antibodies in sera from patients with rheumatoid arthritis or chronic low back pain is low.