EVALUATION OF IGA AND IGG SEROLOGY FOR THE DETECTION OF HELICOBACTER-PYLORI INFECTION

BACKGROUND: Serology is a safe, simple and noninvasive means of determ ining the presence of Helicobacter pylori. Reported sensitivity and sp ecificity, however, have varied tremendously, and it is not clear whet her 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 inf ection and eradication, The kits, Pyloriset EIA-A and EIA-G, use enzym e immunoassay techniques to estimate immunoglobulin (Ig) A and IgG ant ibody titres, respectively, PATIENTS AND METHODS: Consenting adult pat ients referred for upper endoscopy underwent antral biopsies for histo logy and a serum sample for serological testing. The serum samples wer e divided into three groups: group 1 - 17 samples from patients with H pylori detected histologically; group 2 - 13 samples from patients wi th negative histology and no recent (less than three months) eradicati on therapy; and group 3 - six samples from patients in whom H pylori h ad been successfully eradicated one month before serological testing. The ability of IgA and IgG serology to differentiate between the prese nce or absence of H pylori infection was assessed using contingency ta ble analysis. Ideal titre cut-offs were determined using receiver oper ating 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% Cr: 57-96), specificity 85% (55-98) and diagnostic a ccuracy 83% (65-94). For IgG, the sensitivity, specificity and diagnos tic accuracy were 76% (95% CI: 50-93), 85% (55-98) and 80% (61-92), re spectively. IgA levels one month posteradication (group 3) were signif icantly lower (P<0.05) than the titres from the H pylori positive pati ents (group 1), whereas IgG levels were not. CONCLUSIONS: Serology is a simple, noninvasive method of H pylori detection exhibiting good dia gnostic accuracy. The Pyloriset EIA-A assay has test performance chara cteristics similar to the Pyloriset EIA-G. At one month posteradicatio n therapy IgA, but not IgG, detection may be a good method of assessin g : disappearance of H pylori.