[A comparison of two tests for rheumatoid factor: latex test and l-agglutination (author's transl)]

Positive and negative reactions of latex test (LX) and streptococcal L-agglutination (LA) were correlated significantly with one another. However, in approximately 70% of the sera tested only one test was positive, LX at a much higher rate than LA. Postive rheumatoid factor tests were found in 117 patients with rheumatoid arthritis and in 595 patients with other diseases, exclusive of connective tissue diseases. Among the seropositive patients with rheumatoid arthritis, a positive reaction was seen in 85% and 71% by LX or LA respectively. Patients with nonrheumatic diseases showed positive reactions at a rate of 3,1%, with 2,3% and 1,7% in LX or La respectively. This shows that LA is less sensitive, but more specific as compared with LX. With increasing age of the patients, the rate of "nonspecific positive" reactors in patients with nonrheumatic diseases increases, more strongly for LX than for LA. The distribution of positive tests (LX positive, LA positive, or both positive) was analyzed in various groups of patients. The rate of positive reactions in both tests is significantly higher than patients with rheumatoid arthritis; it further increases with the severity of the disease. In cases with positive CRP, the rate of sera positive in both tests is higher, equally in patients with and without rheumatoid arthritis. In patients with nonrheumatic diseases an elevated serum gamma-globulin is associated with positive reactions in both tests and with positive LX. In all other grouping of patients, the rheumatoid factor tests did not yield significant deviations from chance distribution, as determined by chi2 analysis.