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QUESTION: How accurate is the 13C-urea blood test for detecting Helicobacter pylori infection?
Blinded comparison of the 13C-urea blood test with tests based on endoscopic biopsy.
5 centres in the United States (Ann Arbor, Michigan; Syracuse, New York; Gainesville, Florida; Savannah, Georgia; and Los Angeles, California).
121 patients (mean age 49 y, 51% men) who were referred for endoscopy. Exclusion criteria included treatment for H. pylori infection in the previous year or use of antibiotics or bismuth in the previous month or proton-pump inhibitors in the previous 7 days.
Description of tests and diagnostic standards
Patients received 13C-urea, 125 mg dissolved in 75 ml of water. 30 minutes later, a 3-ml blood sample was obtained by venipuncture and analysed by gas isotope ratio mass spectrometry. The 3 diagnostic standards were histological evidence of H. pylori infection in biopsies obtained from the body and antrum of the stomach, a positive result for both histological and rapid urease testing (RUT) (patients with discordant histological and RUT results were considered uninfected), and a positive result for either histological testing or RUT.
Main outcome measures
Sensitivity and specificity for detecting H. pylori infection.
The table shows sensitivities, specificities, and likelihood ratios. Results for the 13C-urea blood test did not differ from those for RUT (p>0.2).
The 13C-urea blood test was similar to rapid urease testing and had high sensitivity and specificity for detecting Helicobacter pylori infection.
Consensus statements in North America and Europe have supported a strategy of “test and eradicate H. pylori” for the management of dyspepsia in the office setting. This strategy benefits patients by breaking the cycle of recurrence of duodenal ulcer disease and decreasing the risk for developing future gastric cancer.1 The cost benefit of this strategy lies in avoiding endoscopy; therefore, accurate and reliable non-endoscopic tests for H. pylori are needed.2
These studies by Chey and colleagues examine the performance of 2 such tests: whole-blood tests done at the point of care to identify antibodies to H. pylori and a 13C-urea blood test. The latter is a new technique based on the 13C-urea breath test in which 13CO2 is released from ingested 13C-urea if H. pylori, with its urease enzyme, is present in the stomach. Rather than requiring pre- and post-breath samples, a single blood test can be done 30 minutes after ingestion to identify 13C-bicarbonate by mass spectrometry.
Important differences exist between the antibody and urease-based technologies. The whole-blood tests give an immediate result and can be done in 5 to 10 minutes. The 13C-urea blood test requires more staff input, a 30-minute delay before sample collection, and fasting for patients. The sample has to be sent to a central laboratory for analysis, and the result and subsequent therapeutic decision are delayed.
The essential question underlying these 2 studies is whether the additional accuracy of the urea blood test is worth the additional cost. This question has 2 parts. First, what is the difference in performance of the 2 tests in the office setting? Second, what patient-related benefits are obtained by that difference? As Chey and colleagues state, no gold standard exists for identifying H. pylori, and most evaluations use a proxy of several reference tests combined. Chey and colleagues' approach is a base-case evaluation that uses histological testing alone with a biopsy-based urease test as an additional reference standard for calculating test performance under the worst and best conditions.
The combination of reference standard error, spectrum bias, and a greater potential for operator error means that caution should be used when extrapolating these results to the office setting.3
Unfortunately, although the absolute values of the performance of the 13C-urea blood test are greater than the whole-blood antibody tests, the confidence intervals overlap, which means that we cannot be certain that the difference is robust. In any case, clinical differences between the 2 types of tests will be small because, at most, only 20% of patients will benefit from the “test and eradicate” strategy,4 and the absolute difference in sensitivity of the tests is only 5% to 10%.1 Only 2 patients in 100 might be missed with the antibody test. An evaluation of the tests in the office setting with larger samples and a health economic analysis are needed before an informed choice can be made between whole-blood tests and 13C-urea–based tests for applying the “test and eradicate” strategy in the office.
Source of funding: not stated.
For correspondence: Dr W D Chey, University of Michigan Medical Center, 3912 Taubman Center, Box 0362, Ann Arbor, MI 48109, USA. FAX 734-936-7392.