Background: The [13C]urea breath test is a convenient method to estimate Helicobacter pylori colonization non-invasively. As an alternative method, the [15N]urea urine test has been established. It is hypothesized that the urine test could be advantageous under some circumstances. The diagnostic value of the breath test might, for example, be jeopardized owing to fluctuating 13C isotope dilution by endogenous carbon dioxide.
Methods: To compare the reliability and practicability of the two tests, 13C breath tests and 15N urine tests were performed simultaneously in three groups of patients: A) 36 adults under standardized conditions, B) 67 children who were allowed to move around during the test, and C) 18 children once without and once during standardized physical activity.
Results: In the 36 adults there was a close correlation of the test results of the two methods (r = 0.88). In contrast, the correlation in the group of 67 children and infants was poor (r = 0.10). In the children with controlled activity the 13C results fluctuated, whereas the 15N results remained unchanged.
Conclusions: Owing to their identical biochemical basis the breath test and the urine test produce the same diagnostic results in the same individuals if standardized pre-test and test conditions are followed. However, factors such as physical activity during the test may provoke fluctuations with a tendency to decreasing 13C values. This could be due to additional isotope dilution by increases in the endogenous production of 12C-carbon dioxide. We conclude that in very active children the 15N urine test might be advantageous and more reliable than the 13C breath test.