THE INFLUENCE OF SIZE OR NUMBER OF BIOPSIES ON RAPID UREASE TEST-RESULTS - A PROSPECTIVE EVALUATION

Background: The optimal number or size of endoscopic biopsies for use in rapid urease testing has not been established. Postulating that inc reasing the amount of tissue sampled would improve diagnostic yield an d hasten development of a positive test, we compared urease testing wi th one regular biopsy, two regular biopsies, and one ''jumbo'' forceps biopsy. Methods: One hundred fifty patients undergoing endoscopy had three sets of prepyloric biopsies placed in a CLOtest: one regular for ceps biopsy, two regular forceps biopsy, and one large-channel jumbo f orceps biopsy. Biopsies were then taken for two independent histologic examinations. Disagreements were resolved by another examiner. Result s: Eighty-nine patients (59%) had Helicobacter pylori infection by his tology; interobserver agreement was 90% with kappa = 0.78. The mean ti me to a positive test was 5.3 +/- 0.9 hours for one regular biopsy, 3. 2 +/- 0.7 hours for two regular biopsies, and 3.8 +/- 0.8 hours for on e jumbo biopsy (p < 0.01 for two regular, one jumbo vs. one regular bi opsy). Compared to one regular biopsy, the urease test was positive at least 30 minutes earlier in 56% of the patients with two regular biop sies and 54% with one jumbo biopsy. Sensitivities for one regular vers us two regular biopsies were 1 hour, 19% versus 33% (p = 0.059); 2 hou rs, 38% versus 49% (p = 0.17); 3 hours, 48% versus 60% (p = 0.18); and 24 hours, 75% versus 79% (p > 0.20). Conclusions: Doubling the amount of tissue in the CLOtest hastens the development of a positive test b y approximately 1 1/2 to 2 hours; tests become positive at least 30 mi nutes earlier in over 50% of the patients. Low cost, ease, and excelle nt specificity make the rapid urease test a valuable diagnostic tool. Nevertheless, if used as a ''rapid'' diagnostic test (read within 3 ho urs of biopsy),it is associated with a false negative rate of approxim ately 40%.