RESUMO
The indirect immunoperoxidase (IIP) method was modified and improved for detecting anti-dsDNA. Using fetal calf serum to block the non-specific antibodies and staining with chromatic substrate solution at pH 6.2, the performance time is substantially decreased and the patterns of positive and negative staining are easily distinguished. IIP was compared with indirect hemagglutination (IHA), latex agglutination (LA) and the standard method indirect immunofluorescent technique (IFT). The sensitivities and specificities of the three methods were studied in 507 sera from various sources. Using IFT as the gold standard, sensitivities of IIP, IHA, LA were 98.18%, 88.18% and 50.91% respectively, and the corresponding specificities were 99.5%, 98.24% and 100%. There was a good correlation between titers of IFT and IIP (Spearman correlation coefficient = 0.77, p < 0.001) with no significant difference between the titer of both tests (Wilcoxon Matched-Pairs Signed-Rank test, p = 0.143). These results indicate that the modified IIP method is both highly sensitive and specific and only needs a light microscope to perform it.