Nine rheumatoid factor assays compared.

In this study we have investigated five quantitative and three semi-quantitative rheumatoid factor assays and the Rose-Waaler assay in 120 patients suffering from rheumatoid arthritis and in 76 with other systemic diseases. All tests measure the IgM anti-IgG antibodies. The correlations between the quantitative tests were all higher than 0.86 and much better than between the quantitative and semi-quantitative tests and the semi-quantitative tests themselves (r between 0.22 and 0.85). The within run and between run precision studies for the quantitative tests showed CV values lower than 16%. In spite of the standardisation on the WHO and the Center of Disease Control Reference Preparation we found important differences in patient results. From an analytical point of view, the quantitative assays for rheumatoid factors show certain advantages over the traditional haemagglutination tests.