COMPARISON OF RHEUMATOID-FACTOR ASSAY SYS TEMS - EVIDENCE AND CRITICAL-EVALUATION OF SENSITIVITY, SPECIFICITY AND THEIR INFLUENCE ON PRE-TEST-PROBABILITY AND POST-TEST-PROBABILITY

In this prospective study, sera of 440 patients with rheumatic and deg enerative joint diseases were tested for the presence of rheumatoid fa ctor (RF). The Latex agglutination test (LFT), Waaler-Rose hemagglutin ation, laser nephelometry and IgM-Enzyme immunoassay (IgM-EIA) were us ed for detecting IgM-rheumatoid factors. In addition, rheumatoid facto r of IgA isotype was measured by an IgA-Enzyme immunoassay. Sensitivit y, specificity, pre-test- and post-test-probability were evaluated bas ed on the data obtained to compare the test systems used. Under prospe ctive patient selection, none of the test systems used reached a sensi tivity of 100% concerning its cut off level. Despite this limitation, latex agglutination and IgM-EIA reached the highest sensitivity. Waale r-Rose test (90,8%) showed the best result for specificity. The IgA-EI A held the third position in sensitivity, specificity and efficiency B y comparing sensitivity with specificity, no test system can be recogn ized as the absolutely best one, since the receiver operating characte ristic curves (ROC) overlapped. Practically rheumatoid factor measurem ent should initially use a highly sensitive assay, such as LFT and IgM -EIA to screen for RE In the case of a positive result a more specific assay should be used, for example laser nephelometry, to confirm the result.