Gastric acid measurement is useful in assessing the effectiveness of antisecretory drugs, however, the conventional tests involve invasive nasogastric intubation. Orally administered 13C-labeled calcium carbonate (Ca13CO3) reacts with gastric acid to produce 13C-labeled carbon dioxide (13CO2), which is then excreted in the breath. The objective of this study was to evaluate the suitability of Ca13CO3 breath test for estimating gastric acid secretion in human noninvasively. First, the Ca13CO3 breath test and the measurement of pooled gastric acid under a fasting condition were performed in 6 healthy volunteers to evaluate the correlation between the two parameters. Next, endoscopic gastric acid collection and the Ca13CO3 breath test were performed on different days after pentagastrin injection in 20 subjects to evaluate the correlation between the tests and the reproducibility. Finally, the same studies were repeated in 4 subjects before and after 1-week rabeprazole, a proton pump inhibitor, administration. The maximum 13CO2 concentration (Cmax) correlated very well with the amount of pooled gastric acid (r = 0.95), suggesting that Ca13CO3 breath test values well reflected the fasting intragastric acidity. The 13CO2 concentration after pentagastrin injection correlated well with pentagastrin-stimulated maximal acid output (r = 0.79 at 20 min). The reproducibility of the Ca13CO3 breath test under pentagastrin-stimulation was good (coefficient of variation = 0.11). Rabeprazole administration markedly reduced the values of the Ca13CO3 breath test, suggesting that it can sensitively assess the efficacy of rabeprazole. The Ca13CO3 breath test can potentially be a useful method for non-invasive estimation for gastric acid secretion in human.
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