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Editor,—The study by Reilly et al(Gut 1997;40:454–8) showing that analysing saliva for the presence of Helicobacter pylori specific antibodies might be useful for diagnosis is interesting and prompted us to investigate the H pylori specific antibody response of the IgA and IgG class in serum and saliva using the immunoblot assay in 90 patients with chronic gastritis who underwent gastroscopy. H pylori carrier status was defined when both histology and urease rapid test were positive. Serum (2 ml) and unstimulated saliva were obtained just before endoscopy and stored at −20°C pending analysis. Total cell lysate of a clinical isolate of H pylori was used as antigen. A serum sample was considered positive by the immunoblot analysis if antibodies could be detected against at least one protein of high molecular mass (87–128 kDa—that is, VacA or CagA) or against at least two proteins of low molecular mass (22–33 kDa—that is, ureaA).1
Although the sensitivity of the IgG immunoblot performed on serum samples was 98.3%, the performance of the IgG immunoblot on saliva was poor. Saliva samples were used first in different dilutions (undiluted, and diluted 1 in 4, 1 in 10) in order to assess the optimum dilution for the immunoblot test. In our study, at the optimum dilution of 1 in 4, the sensitivity was only 20.3%, and the specificity was 96.7%, with positive and negative predictive values of 91.5% and 39.4%, respectively.
Although we used different dilutions of saliva, we could not confirm the results that have been published recently by Reilly et al and other investigators; using the ELISA technique for detection of salivary IgG antibodies against H pylori, a sensitivity of between 71 and 85% has been described by these authors.2-4 By contrast, in terms of specificity the immunoblot assay performed on saliva was better than that for the ELISA tests, which had specificities between 66 and 88%.2-4
In conclusion, although the specificity of detecting salivary H pylori specific IgG antibodies using the immunoblot technique is relatively high, its low sensitivity makes this test unsuitable for diagnosis of H pylori infection in saliva samples.