Effect of immersion of biopsy forceps in formalin on tissue urease activity

Background and Aims: It is routine practice to wash biopsy forceps that hav e been immersed in formalin solution before taking gastric biopsies to test for urease activity as formalin is thought to inactivate the urease enzyme . The aim of this study was to assess the effect of pre-immersion of biopsy forceps in formalin solution on the ability to detect Helicobacter pylori urease activity in biopsies obtained with the same forceps. Methods: Two hundred consecutive patients undergoing gastroscopy who had ma croscopic evidence of possible H. pylori infection had an initial antral bi opsy taken using sterile forceps for determining biopsy urease activity. Th e same forceps were then used to obtain an antral biopsy for histological e xamination. The forceps were then used, without washing off any adherent fo rmalin solution, to obtain a further antral biopsy for urease testing. Results: The concordance rate for urease tests, with or without formalin ex posure, was 100% (95% confidence interval (CI) 98.2-100%). Fifty-six of 200 patients (28%) were found to have urease-positive biopsies. Of these, 52/5 6 (92.9%) had identifiable H, pylori on histopathology. One hundred and for ty-four of 200 patients (72%) were found to have urease-negative biopsies. Of these, seven (4.9%) had identifiable H. pylori on histopathology. Six of seven (85.7%) had only a small number of organisms identified. The sensiti vity and specificity for the urease test compared with the histopathology a s a reference standard was 88.1% (95% CI 79.9-96.4%) and 97.2% (95% CI 94.4 -99.9%), respectively. Conclusion: Immersion of biopsy forceps in formalin did not reduce the abil ity to detect urease activity in gastric biopsies taken subsequently. (C) 1 999 Blackwell Science Asia Pty Ltd.