CLINICAL QUESTION: How does a new whole-blood Helicobacter pylori antibody test compare with quantitative laboratory serology?
BACKGROUND: Baseline screening for H pylori infection with an antibody test is a widely used, reasonably accurate marker of infection, and may be cost-effective.1 Serologic tests require venipuncture, followed by a delay as the serum is either sent to a reference laboratory or the sample is prepared for an in-office test. Whole-blood finger-stick antibody tests offer a simple in-office test with more rapid results, but the first generation of tests were less accurate than laboratory serology. A new whole-blood finger-stick antibody test is now available (StatSimple; Saliva Diagnostic Systems; Vancouver, Washington) that may be more desirable because of its ease of use, low cost, and the lack of a requirement for Clinical Laboratory Improvement Amendment (CLIA) certification.
POPULATION STUDIED: Study participants were scheduled to undergo endoscopy for clinical indications. Patients were excluded for being younger than 18 years; having a history of previous treatment for H pylori; or having used antibiotics, bismuth-containing medications, omeprazole, or lansoprazole in the previous 4 weeks. A total of 201 patients met the inclusion criteria.
STUDY DESIGN AND VALIDITY: All patients had one antral biopsy taken for a rapid urease test and 2 for histologic examination. A finger-stick was performed to obtain 100 mg of blood for the whole-blood antibody test, and venipuncture was performed to obtain serum for a quantitative enzyme-linked immunosorbent assay serologic test. Given the lack of a clear reference standard for a diagnosis of H pylori, each antibody test was measured against 2 reference standards. Reference standard 1, the more sensitive one, consisted of having either a positive rapid urease test result or a positive histologic examination result. Reference standard 2 was more specific but less sensitive and required that both biopsy results were positive. Researchers performing each test were blinded to the results of all other tests.
OUTCOMES MEASURED: The primary outcomes were the sensitivity and specificity of the whole-blood and quantitative serologic antibody tests.
RESULTS: The sensitivities of the whole-blood test and quantitative serology using reference standard 1 (86% vs 92%, P=.19) and the gold reference standard 2 (90% vs 94%, P=.41) were not significantly different. The whole-blood test had similar or slightly greater specificity than the quantitative serology using reference standard 1 (88% vs 77%, P=.052) and the gold standard 2 (79% vs 67%; P=.048). The positive and negative likelihood ratios for the whole-blood test using reference standard 2 were 4.3 and 0.1. Given a prevalence of H pylori infection of 40% (typical of the primary care setting in the United States), a negative test result reduced that likelihood to 6%, and a positive result increased it to 73%.
New-generation finger-stick whole-blood H pylori antibody testing can be simple, inexpensive, and CLIA-exempt, and has a sensitivity and specificity comparable with that of quantitative serologic tests. This test is not useful for following the status of treated patients. Although the authors comment on the finger-stick method being low cost, they did not compare this method with other available diagnostic tests. Other minimally invasive tests are also available. For example, a recent study of a stool immunoassay for H pylori antigen showed excellent sensitivity and specificity (>90%), with costs similar to serologic tests.2 Stool antigen testing could end up being the preferred testing modality because of its combination of low cost, high sensitivity and specificity, minimal invasiveness, and potential for rapid evaluation of efficacy of treatment.