Gastroscopy can flip urea breath test results in patients with low baseline DOB values

A single-center prospective study from China suggests that undergoing gastroscopy can occasionally turn a positive ¹³C-urea breath test negative on repeat testing, and that the risk is concentrated in patients whose initial test values sit close to the diagnostic threshold. The work, published in BMC Gastroenterology, was registered in the Chinese Clinical Trial Registry in January 2024 and enrolled adults scheduled for endoscopy who had tested positive for Helicobacter pylori within the preceding four weeks.

The ¹³C-urea breath test is widely regarded as the gold standard non-invasive method for diagnosing H. pylori infection. Whether undergoing gastroscopy affects the results of a subsequent ¹³C-urea breath test had remained unclear. Whether this actually happens in practice had remained unclear.

The researchers enrolled 93 patients aged 18 to 75 and recorded procedural variables including the pre-endoscopic DOB value, the total volume of saline used to irrigate the stomach during the procedure, procedure duration, the time interval before repeating the breath test, and whether biopsies were taken. The primary outcome was conversion of the breath test from positive to negative after gastroscopy. Twelve patients, or 12.9 percent, converted to negative on retesting.

The comparison between converters and non-converters revealed a striking pattern. Patients who converted had a much lower baseline DOB value, with a median of 6.4 per mille (interquartile range 4.7 to 8.4), compared with 27.9 per mille (interquartile range 15.3 to 43.3) in those who remained positive, a difference that was highly significant. Irrigation volume told the opposite story in the raw data: the non-conversion group received more saline on average, with a median of 100.0 milliliters versus 60.0 milliliters in the conversion group. Age, sex, procedure duration, the retesting interval and biopsy rates showed no significant differences between the groups.

When the variables were entered into a multivariate Firth logistic regression, only the baseline DOB value retained its significance. Each unit increase in DOB was associated with lower odds of conversion, with an odds ratio of 0.739 (95 percent confidence interval 0.616 to 0.885, P = 0.001). Irrigation volume, by contrast, was no longer significant once DOB was accounted for, with an odds ratio of 0.989 (95 percent confidence interval 0.969 to 1.010, P = 0.311).

The authors conclude that a lower baseline DOB value is an independent factor for negative conversion on a subsequent breath test, and they emphasize the need for careful interpretation of post-gastroscopy ¹³C-UBT results, particularly when values lie near the diagnostic threshold. The practical implication is that a negative breath test performed shortly after an endoscopy in a patient whose earlier value was only marginally positive should be interpreted with caution, since the procedure may have contributed to the result rather than a genuine absence of infection.

The study has limitations worth keeping in view. It was a single-center observational trial of 93 patients, and only 12 experienced conversion, which limits statistical power and generalizability. The reported association between DOB and conversion is observational and does not establish a causal mechanism, and the trial was conducted in a Chinese patient population, so the findings may not transfer directly to settings with different H. pylori prevalence or endoscopic practice.

Subject of Research: The effect of gastroscopy on ¹³C-urea breath test results for Helicobacter pylori infection

Article Title: The impact of gastroscopy on the results of ¹³C-urea breath test: a prospective study

Article References: Xiao, L., Ou, Y., Liao, J., & Zeng, X. (2026). The impact of gastroscopy on the results of ¹³C-urea breath test: a prospective study. BMC Gastroenterology. https://doi.org/10.1186/s12876-026-05490-1

Image Credits: AI Generated

DOI: 10.1186/s12876-026-05490-1

Keywords: Helicobacter pylori, urea breath test, gastroscopy, 13C-UBT, delta over baseline, diagnostic accuracy, endoscopy, prospective study, Firth logistic regression, BMC Gastroenterology, impact, results