Evaluation of gastric acid secretion at endoscopy with a modified Congo red test

Markedly decreased or absent gastric acid production is associated with a number of clinically significant conditions, and identification of patients with hypo/achlorhydria may be important. However, current methods of assessing impaired acid secretion are unreliable, time-consuming, and/or complex. The aim of this prospective study was to evaluate a modified endoscopic Congo red test for the diagnosis of hypo/achlorhydria by correlation with a standard gastric acid secretory test.

One hundred six consecutive outpatients with or without dyspeptic symptoms referred for endoscopy were evaluated by using a modified endoscopic Congo red test and a standard test of gastric acid secretion. The modified endoscopic Congo red test suggested hypo/achlorhydria when there was no color shift or a shift of small extent (less than one third of fundic mucosa). Hypo/achlorhydria by the standard gastric acid secretory test was defined as a maximal acid output of less than 6.9 mmol/hour in men and 5.0 mmol/hour in women.

The accuracy of the modified endoscopic Congo red test for the diagnosis of hypo/achlorhydria was 0.98 (95% CI [0.93, 0.99]). The sensitivity was 1.0 (95% CI [0.92, 1.00]) and specificity 0.96 (95% CI [0.88, 0.99]). All patients tolerated the modified endoscopic Congo red test well.

The modified endoscopic Congo red is an accurate, simple, fast, inexpensive, and well-tolerated chromoendoscopic method for identification of patients with hypo/achlorhydria during routine upper endoscopy.