Interference with total hemolytic complement assay in rheumatoid arthritis: correlation with disease activity.

A subgroup of patients with rheumatoid arthritis (RA) whose sera agglutinated sensitized sheep erythrocytes used for total hemolytic complement determination has been identified. These patients have higher titers of rheumatoid factor (RF) and more severe rheumatoid disease compared to controls. The agglutination of sensitized sheep erythrocytes by sera of some patients with RA may be related to qualitative or quantitative variations in their RF.