Association between antinuclear antibody titers and connective tissue diseases in a Rheumatology Department.

OBJECTIVE: To determine the dilution titles at antinuclear antibodies (ANA) by indirect immunofluorescence observed in cell substrate HEp-2 and its association with the diagnosis of systemic connective tissue disease in ANA test requested by a Rheumatology Unit.

METHOD: Samples of patients attended for the first time in the rheumatology unit, without prior ANA test, between January 2010 and December 2012 were selected. The dilution titers, immunofluorescence patterns and antigen specificity were recorded. In January 2015 the diagnosis of the patients were evaluated and classified in systemic disease connective tissue (systemic lupus erythematosus, Sjögren's syndrome, systemic sclerosis, undifferentiated connective, antiphospholipid syndrome, mixed connective tissue and inflammatory myophaty) or not systemic disease connective tissue.

RESULT: A total of 1282 ANA tests requested by the Rheumatology Unit in subjects without previous study, 293 were positive, predominance of women (81.9%). Patients with systemic connective tissue disease were recorded 105, and 188 without systemic connective tissue disease. For 1/640 dilutions the positive predictive value in the connective was 73.3% compared to 26.6% of non-connective, and for values ≥1/1,280 85% versus 15% respectively. When performing the multivariate analysis we observed a positive association between 1/320 dilution OR 3.069 (95% CI: 1.237-7.614; P=.016), 1/640 OR 12.570 (95% CI: 3.659-43.187; P=.000) and ≥1/1,280 OR 42.136 (95% CI: 8.604-206.345; P=.000).

CONCLUSION: These results show association titles dilution ≥1/320 in ANA's first test requested by a Rheumatology Unit with patients with systemic connective tissue disease. The VPP in these patients was higher than previous studies requested by other medical specialties. This may indicate the importance of application of the test in a targeted way.