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

Test meals are used in the urea breath test to slow gastric emptying and to increase the area of contact with the substrate. Recently, citric acid has been suggested as an improved liquid test meal. The mechanism is 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 citric acid test meals on urea hydrolysis in vivo, to identify the possible mechanism for enhanced urea hydrolysis, and to identify the minimum effective dose.

We compared the U.S. commercial 13C-urea breath test with four liquid test meals (200 ml of water) consisting of citric acid, ascorbic acid, sodium citrate, and glucose polymer and also after the subcutaneous administration of pentagastrin. We studied healthy volunteers with and without proven H. pylori infection (by serology and histology). 13C-urea was administered 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 13C-urea.

A dose response in urease activity was evident as the amount of citric acid was increased from 1 to 4 g. Citric acid at 1, 2, or 4 g produced significant increases in breath 13CO2 activity, compared with the commercial pudding (p < 0.05). Ascorbic acid (p = 0.053), subcutaneous pentagastrin (to lower pH) (p = 0.199), and glucose polymer (p = 0.03) (to delay gastric emptying) all approximately doubled breath 13CO2, compared with the commercial kit. Nevertheless, the increases were all significantly less than with the 4 g citric acid test meal.

The data are consistent with the marked effect of citric acid on gastric emptying and, possibly, distribution of the urea within the stomach 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 ml) to enhance the simplicity and palatability of the test.