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Screening for exposure to Helicobacter pylori
Helicobacter pylori is a spiral-shaped, gram-negative bacillus that has been associated with gastritis, gastric and duodenal ulcers, and gastric malignancies.
Helicobacter pylori is found worldwide. In Caucasian populations in the United States and other industrialized countries, Helicobacter pylori infection is infrequent in childhood. Prevalence increases 0.5% to 2% with each year of age, reaching about 50% in those who are 60 or older. Prevalence rates appear to be higher in African American and Hispanic populations as compared to rates among Caucasians; this is thought to be due to socioeconomic status. In a random population of 200 apparently healthy blood donors tested for Helicobacter pylori IgG antibody, the positivity rate was 27.5%.
The gold standard for diagnosis of Helicobacter pylori disease is gastric biopsy and evaluation for the presence of spirochetes by gram, silver, giemsa, or acridine orange stains. Alternatively, biopsied tissue can be examined by immunofluorescence or immunoperoxidase methods, rapid urease testing, and/or culture.
Exposure to Helicobacter pylori can be determined by detection of IgA, IgG, or IgM-class serum antibodies to the organism. Screening patients for the presence of antibodies to Helicobacter pylori is a convenient, noninvasive means for assessing whether a patient has been exposed to Helicobacter pylori and whether gastrointestinal symptoms may be related to Helicobacter pylori infection. Because serology may lack specificity and does not distinguish between recent or remote infection, active disease is best diagnosed by the Helicobacter pylori stool (HPSA / Helicobacter pylori Antigen, Feces) antigen assay or by the Helicobacter pylori urea breath test (UBT / Helicobacter pylori Breath Test).
See Helicobacter pylori Diagnostic Algorithm in Special Instructions.
Negative (Results with index values of <8.95 are negative.)
Patients with Helicobacter pylori infection nearly always develop IgG class antibodies. However the presence of IgG-class antibodies does not distinguish between remote exposure to Helicobacter pylori and acute, ongoing infection. If clinically indicated, additional tests including either the urea breath test or the stool antigen assay should be performed to determine infection status.
This assay should be performed only on patients with gastrointestinal symptoms and should not be used to test asymptomatic patients.
A positive test result does not distinguish between colonization or infection by Helicobacter pylori and does not indicate the presence of gastrointestinal disease. It should be used as an aid to the detection of such disease with other clinical tests such as the urea breath test or stool antigen assay.
A negative result does not preclude the absence of antibodies to Helicobacter pylori. Colonization may be present, however it may be in its very early stages or the antibody titer may be too low for the assay to detect.
To evaluate the accuracy of the Biomerica Helicobacter pylori IgG GAP EIA, 200 prospective serum samples submitted for routine Helicobacter pylori IgG testing by the VIDAS enzyme-linked fluorescence immunoassay (ELFA, bioMerieux, Durham, NC) were also analyzed in a blinded fashion by the Biomerica assay within the same 24 hour period. Samples with discordant results after initial testing were repeated by both assays and further resolution of discrepant results was performed by an alternative assay (ImmunoComb H. Pylori IgG, Wampole Laboratories, Alere, Waltham MA). The results are summarized below:
Table 1. Comparison of Biomerica vs. bioMerieux EIAs for detection of Helicobacter pylori IgG
Helicobacter pylori GAP IgG EIA
bioMerieux Helicobacter pylori IgG EIA
(a) One of 4 samples were negative by the Wampole EIA
(b) One of 14 samples was quantity not sufficient (QNS) for testing by Wampole. Four of 13 samples were positive and 2 of 13 samples were equivocal by the Wampole EIA.
Sensitivity: 92.0% (46/50); 95% Confidence Interval (CI): 80/7-97.4%
Specificity: 90.3 (131/145); 95% CI: 84.3%-94.3%
Overall percent agreement: 88.5% (177/200); 95% CI: 83.3%-92.3%
Following discordant resolution testing by the Wampole assay, sensitivity, specificity and percent agreement were adjusted to 94.2% (49/52), 93.6% (132/141), and 90.5% (181/200), respectfully.
In a random population of 100 apparently healthy blood donors tested for Helicobacter pylori IgG antibody using the Biomerica Helicobacter pylori GAP IgG EIA, the positive rate was 19%, which is consistent with previous findings.(1)
Couturier MR: The evolving challenges of Helicobacter pylori disease, diagnostics, and treatment, part 1. Clinical Microbiology Newsletter. 2013;35(3):19-23