Current issues of ACP Journal Club are published in Annals of Internal Medicine


Diagnosis

The 13C-urea blood test is accurate for detecting Helicobacter pylori infection

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ACP J Club. 2000 Jan-Feb;132:35. doi:10.7326/ACPJC-2000-132-1-035

Related Content in this Issue
• Companion Abstract and Commentary: Whole-blood antibody tests were not highly sensitive for detecting Helicobacter pylori infection


Source Citation

Chey WD, Murthy U, Toskes P, Carpenter S, Laine L. The 13C-urea blood test accurately detects active Helicobacter pylori infection: a United States, multicenter trial. Am J Gastroenterol. 1999 Jun;94:1522-4. [PubMed ID: 10364016]


Abstract

Question

How accurate is the 13C-urea blood test for detecting Helicobacter pylori infection?

Design

Blinded comparison of the 13C-urea blood test with tests based on endoscopic biopsy.

Setting

5 centers in the United States (Ann Arbor, Michigan; Syracuse, New York; Gainesville, Florida; Savannah, Georgia; and Los Angeles, California).

Patients

121 patients (mean age 49 y, 51% men) who were referred for endoscopy. Exclusion criteria included therapy 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 analyzed by gas isotope ratio mass spectrometry. The 3 diagnostic standards were histologic evidence of H. pylori infection in biopsies obtained from the body and antrum of the stomach, a positive result for both histologic and rapid urease testing (RUT) (patients with discordant histologic and RUT results were considered uninfected), and a positive result for either histologic testing or RUT.

Main outcome measures

Sensitivity and specificity for detecting H. pylori infection.

Main results

Sensitivities, specificities, and likelihood ratios are shown in the Table. Results for the 13C-urea blood test did not differ from those for RUT (P > 0.2).

Conclusion

The 13C-urea blood test was similar to rapid urease testing and had high sensitivity and specificity for detecting Helicobacter pylori infection.

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.


Table. Test characteristics for detecting Helicobacter pylori infection*

DiagnostIc standards Tests Sensitivity (95% CI) Specificity (CI) +LR -LR
Histologic testIng 13C-UBT 89% (85 to 93) 96% (94 to 98) 19.9 0.1
RUT 87% (75 to 95)† 96% (87 to 99)† 19.4† 0.1†
Histologic testing and RUT 13C-UBT 94% (87 to 100)‡ 91% (85 to 97)‡ 10.4 0.1
Histologic testing or RUT 13C-UBT 88% (80 to 96)‡ 98% (95 to 100)‡ 44.0 0.1

*13C-UBT = 13C-urease blood test; RUT = rapid urease testing. LRs defined in Glossary and calculated from data in article.
†Calculated from data supplied by author.
‡CIs provided by author.


Commentary

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 nonendoscopic 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 histologic 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.

Brendan Delaney, MD, BMBCh
University of Birmingham
Birmingham, England, UK


References

1. Calam J. Clinicians’ guide to Helicobacter pylori. London: Chapman and Hall; 1996.

2. Heaney A, Collins JS, Watson RG, et al. A prospective randomised trial of a “test and treat” policy versus endoscopy based management in young Helicobacter pylori positive patients with ulcer-like dyspepsia, referred to a hospital clinic. Gut. 1999;45:186-90.

3. Irwig L, Tosteson AN, Gatsonis C, et al. Guidelines for meta-analyses evaluating diagnostic tests. Ann Intern Med. 1994;120:667-76.

4. McColl K, Murray L, El-Omar E, et al. Symptomatic benefit from eradicating Helicobacter pylori infection in patients with nonulcer dyspepsia. N Engl J Med. 1998;339:1869-74.