| PASSIVE TESTING
Serology – Historically, serologic assay for immunoglobulin G (IgG) antibodies to H. pylori by enzyme-linked immunosorbent assay (ELISA) testing
had been recommended for screening prior to therapy. However due to its high rate of false positives and false negatives, it is no longer reliable for use in primary care settings. Antibodies are present in serum about 21 days after infection and can remain present long after the organism is eradicated. Therefore, serology cannot be used to assess whether the H. pylori infection is active, past exposure has occurred or if eradication of H. pylori has taken place. For this reason, a positive serologic result is not proof of active infection. Further, serologic testing is less specific and sensitive than active tests (i.e., the stool antigen and urea breath tests). In fact, the overall accuracy of serology tests may not be adequate for clinical decision-making (see accompanying table “Accuracy of noninvasive tests for H. pylori infection”). Thus, serologic testing cannot be used to confirm eradication of H. pylori infection or to test patients who have previously been infected.
TESTING FOR ACTIVE H. pylori INFECTION
Antigen Test – Fecal antigen testing by enzyme immunoassay or immunochromatography ( HpSA ® ) is one of the simplest and least expensive methods available. It is as simple and noninvasive as serology, can be used regardless of prior testing or treatment, and detects active infection as effectively as urea breath testing with less potential for false negative results while taking acid suppression or bismuth medications. 7The sensitivity and specificity of fecal antigen testing exceed 90%.
Results of the fecal antigen test aid in the definitive diagnosis of active H. pylori infection, can be used to monitor response during and post treatment, and can confirm eradication of H. pylori. Confirmation of eradication should be performed 1 month after eradication therapy has been completed and testing for H. pylori should not be performed until 2 weeks after stopping proton pump inhibitor therapy. More information is available on the HpSA® website.
Urea Breath Test – The Urea Breath Test (UBT) measures the radio-labeled carbon dioxide formed in the stomach when the urease produced by H. pylori breaks down a sample of C13 or C14-labeled urea. Breath testing requires that the patient ingest a standard sample of labeled C13 or C14 and, at a predetermined time, produce a breath sample. After collection, the breath sample is analyzed by means of a mass spectrometer or scintillation counter.
One limitation of this method is the possibility of false negative results when antibiotics used to eradicate H. pylori or proton pump inhibitors used to heal ulcer disease are taken in the period before testing. Breath testing is more expensive than serology or fecal antigen testing but less expensive than invasive (endoscopy) testing.