Citric acid as the test meal for the C-13-urea breath test

OBJECTIVE: Test meals are used in the urea breath test to slow gastric empt ying and to increase the area of contact with the substrate. Recently, citr ic acid has been suggested as an improved liquid test meal. The mechanism i s unknown and could act by delaying gastric emptying, decreasing the pH at the site of the bacteria, or both. Our aim was to evaluate the effects of c itric acid test meals on urea hydrolysis in vivo, to identify the possible mechanism for enhanced urea hydrolysis, and to identify the minimum effecti ve dose. METHODS: We compared the U.S. commercial C-13-urea breath test with four Li quid test meals (200 ml of water) consisting of citric acid, ascorbic acid, sodium citrate, and glucose polymer and also after the subcutaneous admini stration of pentagastrin. We studied healthy volunteers with and without pr oven H. pylori infection (by serology and histology). C-13-urea was adminis tered orally simultaneously with the liquid test meals or immediately after the pudding had been ingested. Breath samples were taken before and after oral administration of the C-13-urea. RESULTS: A dose response in urease activity was evident as the amount of ci tric acid was increased from 1 to 4 g. Citric acid at 1, 2, or 4 g produced significant increases in breath (CO2)-C-13 activity, compared with the com mercial pudding (p < 0.05). Ascorbic acid (p = 0.053), subcutaneous pentaga strin (to lower pH) (p = 0.199), and glucose polymer (p 0.03) (to delay gas tric emptying) all approximately doubled breath (CO2)-C-13, compared with t he commercial kit. Nevertheless, che increases were all significantly less than with the 4 g citric acid test meal. CONCLUSIONS: The data are consistent with the marked effect of citric acid on gastric emptying and, possibly, distribution of the urea within the stom ach being largely responsible for the enhanced urease activity with citric acid test meals. It should be possible to use a low dose of citric acid (e. g., 1 g per 200 mi) to enhance the simplicity and palatability of the test. (C) 1999 by Am. Cell. of Gastroenterology.