Detection of Helicobacter pylori by rapid urease tests: is biopsy size a critical variable?

Background: The variables responsible for false-positive and false-negative rapid urease tests are largely unexplored. Objectives: We compared the results of rapid urease testing with jumbo cup forceps (3.3 mm diameter) and tiny cup forceps (1.8 mm diameter) with two rapid urease tests. Methods: Antral biopsies were obtained. The order of forceps and rapid urease tests was randomized. Biopsies were also taken for Genta staining. Results: One hundred and two patients were studied; 59 had Helicobacter pylori infection. There were 22 false-negative tests (8 CLOtest, 16 hpfast) and 5 false-positive tests (3 CLOtest, 2 hpfast). All 5 false-positive tests were among those positive only in the second 12 hours. There was no difference in results with the jumbo and tiny cup forceps. Five percent to nine percent (average, 6.6%; 95% confidence interval, 4.4% to 9.6%) of tests with any of the combinations gave an erroneous categorization of H. pylori status. There were no clinical or statistical differences in H. pylori categorizations by CLOtest or hpfast. Conclusion: The diagnostic yield for detecting H. pylori infection by rapid urease tests is not adversely affected by small biopsy size, possibly because tiny biopsies obtain superficial tissue where H. pylori reside.