Evaluation of IgA and IgG serology for the detection of Helicobacter pylori infection

Abstract

Background: Serology is a safe, simple and noninvasive means of determining the presence of Helicobacter pylori. Reported sensitivity and specificity, however, have varied tremendously, and it is not clear whether positive serology reflects previous infection (treated within the past one to two years) or ongoing infection. Objectives: To assess the usefulness of two commercial kits to detect both ongoing H pylori infection and eradication. The kits, Pyloriser EIA-A and EIA-G, use enzyme immunoassay techniques to estimate immunoglobulin (Ig) A and IgG antibody titres, respectively. Patients and Methods: Consenting adult patients referred for upper endoscopy underwent antral biopsies for histology and a serum sample for serological testing. The serum samples were divided into three groups: group 1 - 17 samples from patients with H pylori detected histologically; group 2 - 13 samples from patients with negative histology and no recent (less than three months) eradication therapy; and group 3 - six samples from patients in whom H pylori had been successfully eradicated one month before serological testing. The ability of IgA and IgG serology to differentiate between the presence or absence of H pylori infection was assessed using contingency table analysis. Ideal titre cut-offs were determined using receiver operating characteristic curve analysis. Results: The ideal cut-off titres for IgA and IgG were 300 and 900 U, respectively. The sensitivity for IgA was 82% (95% CI: 57-96), specificity 85% (55-98) and diagnostic accuracy 83% (65-94). For IgG, the sensitivity, specificity and diagnostic accuracy were 76% (95% CI: 50-93), 85% (55-98) and 80% (61-92), respectively. IgA levels one month posteradication (group 3) were significantly lower (P < 0.05) than the titres from the H pylori positive patients (group 1), whereas IgG levels were not. Conclusions: Serology is a simple, noninvasive method of H pylori detection exhibiting good diagnostic accuracy. The Pyloriser EIA-A assay has test performance characteristics similar to the Pyloriser EIA-G. At one month posteradication therapy IgA, but not IgG, detection may be a good method of assessing disappearance of H pylori.