The cut-off point of Anti-dsDNA test by EliA dsDNA

Objective: To determine the cut-off point of anti-dsDNA for screening by EliA dsDNA. Methods: Serum specimens requested for anti-dsDNA between October and December 2007 were recruited and tested by the Crithidia luciliae immunofluorescence test (CLIFT) and automated fluorescence immunoassay (EliA dsDNA). The CLIFT was considered as the gold standard method. Different levels of sensitivity and specificity were determined and the cut-off point was selected from among them. Results: Of the 133 specimens collected, 35 were positive whereas 98 were negative with the CLIFT. Of those 35 positive specimens, 2, 0, 2, 2 and 29 were, respectively, in ranges of < 5, 5 to 9.9, 10 to 14.9, 15 to 19.9 and > 20 IU/ml by EliA dsDNA. Also, of the 98 negative specimens, 73, 7, 4, 4 and 10 were, respectively, in ranges of < 5, 5 to 9.9, 10 to 14.9, 15 to 19.9 and > 20 IU/ml by EliA dsDNA. The sensitivity and specificity for each level were determined and the value of 11 IU/ml was selected as the cut-off point. Additionally, when clinical diagnosis was used in specimens with discrepant results, the sensitivity of EliA dsDNA was far better than the CLIFT, whereas the specificity of both methods was comparable. Conclusion: The appropriate cut-off point of EliA dsDNA for screening was 11 IU/ml. Furtermore, the diagnostic value of EliA dsDNA was better than the CLIFT when clinical diagnosis was included in the gold standard criteria.

The effect of antinuclear antibody patterns on antineutrophil cytoplasmic antibody test.

Antineutrophil cytoplasmic antibody (ANCA) is used to diagnose and monitor activity in the primary systemic small vessel vasculitides. Serum samples with antinuclear antibody (ANA) interfere with the reading of neutrophil indirect immunofluorescence. The question arises, will ANA pattern affect the results of ANCA test differently?. To answer this question, documents were retrospectively reviewed for the criteria of ANCA test with positive ANA from January 1 to December 31, 2000. Of 137 serum specimens with ANCA and ANA tests, 58 were positive for ANA test. The result showed that the number of positive P-ANCA with homogeneous pattern of ANA (88.9%) was statistically higher than that with speckled pattern (38.78%). In conclusion, there is a different effect of various ANA patterns on ANCA results. A further prospective study is required to confirm this result.