Health Questions and Answers

Question: How is Helicobacter pylori diagnosed noninvasively?

Answer:

Serology-IgG or IgA antibodies directed at various bacterial antigens can be detected by enzyme-linked immunosorbent assay (ELISA) in serum of infected individuals. In addition, several office-based serologic methods are commercially available. Serologic methods detect evidence of primary H. pylori infection in untreated people with sensitivity and specificity >90%. Although antibody levels may fall after successful bacterial eradication, they remain elevated for up to 3 years. This “serologic scar” limits the usefulness of serology in assessing treatment and determining reinfection as well as reduces the positive predictive value of the test, especially in areas of the world (such as the United States) where prevalence of infection is low. For this reason a positive serology result should be confirmed with a test of active infection, such as a stool or urea breath test before treatment is initiated.

Urea breath or blood tests are ideally suited to make a primary diagnosis of infection, to monitor treatment response, and to assess reinfection, because they are positive only in a setting of active infection. The patient ingests a small amount of carbon-labeled (13C or 14C) urea. The urease of H. pylori hydrolyzes the urea and liberates labeled carbon dioxide, which is absorbed and exhaled in the breath. Labeled carbon dioxide can be collected and quantified in breath or blood samples. Sensitivity and specificity of urea breath or blood testing are >95%. Certain medications can influence test results.

Stool antigen testing is becoming increasingly popular. It is accurate (sensitivity and specificity = 90% and 98%, respectively) and inexpensive. The test is based on polymerase chain reaction amplification of specific H. pylori antigens in stool samples. Stool antigen testing is useful in primary diagnosis and confirmation of eradication of the organism after antibiotic treatment. Certain medications can influence test results

Reference:
Vaira D, Gatta L, Ricci C, Miglioli M: Review article: Diagnosis of Helicobacter pylori infection. Aliment Pharmacol Ther 16(Suppl 1):16-23, 2002.

One Response to “Question: How is Helicobacter pylori diagnosed noninvasively?”

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