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

It is routine practice to wash biopsy forceps that have 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.

Two hundred consecutive patients undergoing gastroscopy who had macroscopic evidence of possible H. pylori infection had an initial antral biopsy taken using sterile forceps for determining biopsy urease activity. The same forceps were then used to obtain an antral biopsy for histological examination. The forceps were then used, without washing off any adherent formalin solution, to obtain a further antral biopsy for urease testing.

The concordance rate for urease tests, with or without formalin exposure, was 100% (95% confidence interval (CI) 98.2-100%). Fifty-six of 200 patients (28%) were found to have urease-positive biopsies. Of these, 52/56 (92.9%) had identifiable H. pylori on histopathology. One hundred and forty-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 sensitivity and specificity for the urease test compared with the histopathology as a reference standard was 88.1% (95% CI 79.9-96.4%) and 97.2% (95% CI 94.4-99.9%), respectively.

Immersion of biopsy forceps in formalin did not reduce the ability to detect urease activity in gastric biopsies taken subsequently.