Chicken antibodies: a tool to avoid false positive results by rheumatoid factor in latex fixation tests

19 rheumatoid factor (RF)-positive sera (Waaler-Rose test) and ten control sera were tested in latex agglutination. All RF-positive sera agglutinated latex particles coated with the different mammalian IgGs (cow, horse, human, mouse, sheep and rabbit) and with chicken anti-human C3 (which was used as a positive control), but none of them with non-specific chicken IgG. The control sera were all negative except when tested with chicken anti-human C3. Chicken antibodies should therefore be useful in assays were RF could interfere and give false positive reactions (e.g., nephelometry, latex agglutination or ELISA).