New non-invasive test of gastric acid secretion for use in children.

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Abstract
Loss of the gastric acid barrier may lead to recurrent enteric infections, small intestinal bacterial overgrowth, persistent diarrhoea, and thus malnutrition. To investigate this possibility, a new, non-invasive test of gastric acid secretion was developed ideal for field use in the developing world, where chronic diarrhoea and undernutrition are common. The test relies on the capacity of the kidney to retain H+ during gastric acid secretion, leading to a post-prandial urine 'alkaline tide'. Gastric intubation studies of seven healthy adult volunteers showed a direct relation between changes in gastric acid secretion and changes in urine acid output (measured as the H+/creatinine molar ratio in spot urine samples). Subjects who secreted gastric acid in response to stimulation with a sham feed showed a fall in urine acid output > 0.5 mmol H+/mmol creatinine (range -7.4 to -1.52 mean -1.12). The most reproducible decrease in urine acid output in response to normal food was observed around the time breakfast was usually eaten and was abolished by 36 hours of treatment with ranitidine. Breakfast time reductions in postprandial urine acid output in 22 healthy English children were comparable with those in healthy adults, and significantly different from values in achlorhydric adults. They were much more variable, however, in 106 Gambian children in whom values spanned both normochlorhydric and achlorhydric ranges (-12.7 to +1.8). Measuring changes in urine acid output at breakfast time provides a reliable indirect measure of gastric acid secretion that can be used in field conditions, enabling the relation between gastric acid output and the development of diarrhoeal diseases to be investigated.