Different strategies in the laboratory diagnosis of autoimmune disease: immunofluorescence, enzyme-linked immunosorbent assay or both?

We investigated the clinical utility of different strategies for antinuclea r antibodies (ANA) and antibodies to extractable nuclear antigens (ENA) tes ting. All requests for ANA and ENA (n=485) in a 20-week period were tested by immunofluorescence (FANA) and immunodiffusion (strategy 1), enzyme-linke d immunosorbent assay (ELISA) techniques (strategy 2) or a combination of F ANA and ELISA (strategy 3). Results of strategy 1 were positive by FANA in 8% (by immunodiffusion in 2%). By ELISA, 11% of the samples tested positive . In 12% (n = 60) of the cases the two strategies did not agree. The positi ve predictive value (PPV) for autoimmune disease of strategy 1 was signific antly higher than that for strategy 2, but after exclusion of rheumatoid ar thritis this difference was abolished. In strategy 2 reagent costs were hig h but working time comparably shorter. With strategy 3 PPV results were not better, whereas costs and working time were higher. The most frequently oc curring reasons for ANA/ENA test requests were: joint symptoms (37%), follo w up (30%) or abnormal laboratory result (7%). In a survey of the clinician s 66% replied that the test result did not have any consequences, irrespect ive of the result or the strategy used. We conclude that FANA and immunodif fusion are superior to ELISA techniques. However, the clinical value of ANA /ENA testing is low and more selective lest ordering is strongly recommende d.