Efficacy of enzyme immunoassay for the detection of Helicobacter pylori antigens in frozen stool specimens: local validation.

Aim: To investigate the efficacy of measurement of Helicobacter pylori stool antigen (HpSA) using stored frozen stool specimens, and to assess whether there were factors affecting efficacy in Hong Kong.

Methods: Patients undergoing upper endoscopy at Tuen Mun Hospital were recruited. Stool samples were saved for HpSA testing and questionnaires were completed. Stool samples were frozen immediately upon receipt and stored at -70 degrees C until tested. HpSA results were compared with rapid urease test and histology.

Results: One hundred and eighty-one patients were recruited. One hundred and seventy-eight patients were suitable for analysis. Eighty-three were H. pylori positive and 95 were H. pylori negative. The mean duration of storage of the stool samples was 120 days (range, 40-225 days). The sensitivity, specificity and positive and negative predictive values were 84.3%, 97.9%, 97.2% and 88.6%, respectively. In patients with a false negative HpSA test, there was a significant delay in collecting the stool specimen after endoscopy when compared with those with a true positive HpSA test (4.2 vs. 2.3 days; P < 0.05). However, the duration of storage of the specimens was not longer, and consumption of coffee or tea and smoking habits were similar.

Conclusions: HpSA testing showed good sensitivity and specificity, even with frozen stool samples stored for up to 225 days. The efficacy was not affected by coffee, tea or smoking.