Reliability of Helicobacter pylori and CagA Serological Assays

Abstract

Background serological assays for Helicobacter pylori are commonly used without knowledge of reliability. This information is needed to define the ability of serological tests to determine either new cases of infection or loss of infection in longitudinal studies. We evaluated the reproducibility and the interrelationships of serological test results for H. pylori and cytotoxin-associated gene product A (CagA) enzyme-linked immunoassays within a subset of participants in a population-based study. Stored samples from 1,229 participants in the third U.S. National Health and Nutrition Examination Survey were replicate serologically tested for H. pylori and CagA. Overall disagreement was 3.4% between duplicate tests for H. pylori (or 2.3% if equivocal results were disregarded). Six percent of samples positive on the first test had an immune serum ratio at least 30% lower on repeat testing. The odds ratio for H. pylori seropositivity on retesting was 2.8 (95% confidence interval [CI] ‫؍‬ 1.8 to 4.5) when CagA serology was positive versus when it was negative. CagA antibody was found among 47.8% of H. pylori-equivocal and 7.0% of H. pylori-negative samples. CagA-positive yet H. pylorinegative samples were more likely to occur among Mexican Americans (odds ratio, 5.2; 95% CI ‫؍‬ 2.4 to 11.4) and non-Hispanic blacks (odds ratio, 5.5; 95% CI ‫؍‬ 2.3 to 13.0) than among non-Hispanic whites. Relying on repeated H. pylori serological tests over time to determine infection rates may result in misinterpretation due to limits in test reproducibility. CagA testing may have a role in verifying infection.

Comparative proteomics and immunoproteomics of Helicobacter pylori related to different gastric pathologies☆

“…This is an important novelty of our approach. In fact, there are significant geographical differences between the clinical manifestations of H. pylori infections; the link between strain specificity [48] and risk of gastric cancer within specific geographical populations [49,50] has been recently reported. In addition, the use of heterologous strains in diagnostic serological tests was envisaged [51,52].…”

High incidence of t(11;18)(q21;q21) in Helicobacter pylori-negative gastric MALT lymphoma

“…CagA is highly immunogenic, and antibodies to CagA are frequently detected in patient's sera that are negative for H pylori IgG antibody. 18 H pylori detection by histologic and immunohistochemical examination is less sensitive and is often affected by the quality and nature of biopsies, but nonetheless it can diagnose around 70% of cases. 19 In the present series, multiple biopsies obtained at various stages of patient's treatment were available in each case, and all biopsies consistently showed absence of H pylori infection.…”

Relation of Serum Ascorbic Acid toHelicobacter pyloriSerology in US Adults: the Third National Health and Nutrition Examination Survey

“…Of the 4557 participants who were H. pylori negative, 461 had a positive serologic test for CagA antigen, i.e., an ostensible false positive rate of 10.1%. In additional recently published analyses that examined the test reliability of the serologic assays, repeat CagA serologies were performed among participants who tested positive, equivocal and negative to the CagA subtype [29]. Reproducibility for the CagA antibody test was 93.4% if the initial H. pylori test was positive, 91.1% if it was equivocal and 86.3% if it was negative [29].…”