349 Detection of Anti-nucclear Antibodies (ana) Used for Diagnostic Approach of Systemic Autoimmune Diseases. Correlation with Double Stranded DNA (DSDNA) and Extractable Nuclear Antigen (ENA) Antibodies

BACKGROUND: To determine the correlation between the titer of ANA and anti-dsDNA and anti-ENA antibodies and the contribution of ANA detection to the diagnosis of connective tissue diseases (CTD). METHODS: Our samples consisted of 516 specimens, from Rheumatology Department, collected during January 2010 – July 2010. The detection of ANA was performed using indirect immunofluorescence (IFA) and the detection of anti-dsDNA and anti-ENA using ELISA. RESULTS: Of the 364 (70.54%) samples with negative ANA 4 (1%) had positive anti-ENA and 2 (0.5%) had positive anti-dsDNA while positive anti-ENA and anti-dsDNA were detected in the 44.73% (n = 68) and 21% (n = 32) of the specimens with positive ANA respectively. The probability of detecting positive anti-ENA and anti-dsDNA rises proportionately to the titer of ANA. Specifically, the correlation between the probability of detecting positive anti-ENA and the titer of ANA is 0.577 (P < 0.001) while the correlation between the probability of detecting positive anti-dsDNA and the titer of ANA is 0.18 (P = 0.003). Probability calculations on the basis of the ANA titer showed that samples with low titer ANAs (1:160 or less) had low probabilities for positive anti-ENA. The receiver operating (ROC) curves of the ANA titer for anti-ENA had a larger under the curve area compared to the ROC curve for anti-dsDNA, indicating that ANA titer is better for predicting anti-ENA than anti-dsDNA. The sensitivity of positive ANA in the prediction of the anti-ENA and anti-dsDNA was 94.40% and 94.10%, the specificity was 81% and 75.10%, the positive prognostic value was 44.70% and 21.10% and negative prognostic value was 98.90 and 99.50%. CONCLUSIONS: The detection of ANA using indirect IFA has high sensitivity in predicting the presence of specialized antibodies and may be used as a screening method for the diagnosis of CTD. It is cost and time effective too. Our study also shows that the ANA titer is useful in predicting anti-ENA. Samples with low titer ANAs (1:160 or less) may not need a further test for anti-ENA unless an ANA-associated disease is highly suspected. However a test for anti-dsDNA should be considered in positive ANA samples at any titer including low titers.