Long-term follow-up study of serum immunoglobulin G and immunoglobulin A antibodies after Helicobacter pylori eradication.

OBJECTIVE: There have been few studies concerning serum titers of anti-Helicobacter pylori immunoglobulin G (IgG) antibody >12 months after eradication of the original infection. Moreover, clinical usefulness of immunoglobulin A (IgA) antibody levels remains to be established. The purpose of this study was to investigate long-term responses of serum IgG-specific and IgA-specific antibodies to H pylori in children after eradication therapy. STUDY
DESIGN: A total of 34 children, 2 to 17 years of age (mean: 11.7 years) with H pylori-associated gastroduodenal disease received eradication therapy (proton pump inhibitor-based dual or triple regimens). Diagnoses included nodular gastritis (n = 8), gastric ulcer (n = 7), and duodenal ulcer (n = 19). Upper gastrointestinal endoscopy and biopsy were performed before the therapy and at 1 to 2 months' posttreatment. H pylori infection and eradication were defined by biopsy-based tests; eradication was successful in 28 patients and unsuccessful in 6. Pretreatment IgG was positive in 30 patients (88. 2%), and the IgA was positive in 31 (91.2%), who were entered into this study (duration </=24 months). Serum samples were obtained before treatment and at 1, 3, 6, 12, 18, and 24 months' posttreatment. IgG and IgA antibodies were measured using commercial enzyme immunoassay kits (HM-CAP and PP-CAP; Enteric Products, Inc, New York, NY).
RESULTS: Compared with pretreatment values, IgG and IgA antibodies significantly and steadily decreased at 1 through 24 months' posttreatment in successfully treated patients. A decrease in titer of the IgA class was significantly greater than that of the IgG class at 1 to 12 months' follow-up. There was no significant decrease in titer of either antibody in all but 2 patients with eradication failure. A >/=30% decrease in titer of the IgA antibody at 6 months indicated eradication with sensitivity of 90.5% and specificity of 100%. For the IgG antibody, a 30% decrease at 12 months showed equal sensitivity and specificity. Seroreversion rates of IgG and IgA antibodies were 53% and 48% at 12 months and were 86% and 81% at 24 months, respectively. The mean periods from the completion of eradication therapy to seroreversion of IgG and IgA antibodies were 11.2 +/- 7.0 and 11.6 +/- 7.8 months, respectively (not significantly different). A higher pretreatment titer of IgG antibody was related to a longer period of seroreversion (r = 0.44). In one patient, (13)C-urea breath test-confirmed reinfection was accompanied by reappearance of significant titers of the IgG and IgA antibodies.
CONCLUSIONS: A serology test is useful for evaluating eradication in children. Approximately half of patients with successful eradication remained to be IgG-seropositive and IgA-seropositive at 12 months' posttreatment. When a decrease titer in antibody is used for assessing eradication, an endpoint of >/=6 months is required. The IgA antibody may be a more convenient indicator of H pylori status than is the IgG antibody.