Epidemiology of the Sheep Cell Agglutination Test

Abstract

The titer of the rheumatoid serum factor detected by sheep cells sensitized by rabbit hemolysin was determined in subjects aged 55 to 64 years in 7 European population samples. Positive titers occurred in 1.6 to 5.4% of the subjects tested. The prevalence of positive tests was significantly greater in urban than in rural populations. In these samples, the proportion of positive reactors was similar in males and females. In an urban sample including all age groups over 15 years, positive tests were also equally distributed among males and females; but in the single rural sample with this age range positive tests occurred more frequently in females than in males. The prevalence of positive tests increased with age in 2 urban samples; a similar result was obtained among females, but not among males, in the single rural sample. The titer distribution curve in rural and urban populations suggests that the serum factor is a continuous variable present in some degree in 17 to 40% of adults and possibly more. The titer was determined in the first-degree relatives of 261 members of an urban population sample. Positive titers occurred in 3% of relatives of propositi with a titer of up to 4, and in 12% of relatives of propositi with a titer of 128 and more. Since positive tests in both husband and wife were not found more frequently than would be expected by chance, it was concluded that genetic rather than environmental factors were responsible for the observed familial aggregation of positive titers. Only about 20% of sero-positive individuals in random samples presented evidence of rheumatoid arthritis as defined by the criteria of the American Rheumatism Association.