Helicobacter pylori Stool Antigen Test: Validation Study Using a Selected Group of Sri Lankan Patients

The use of Helicobacter pylori stool antigen test is limited in Sri Lanka. The validity of the amplified IDEIA HpSt AR monoclonal antibody test was examined in 51 patients who underwent upper gastrointestinal endoscopy and multiple gastric biopsies for dyspeptic symptoms. Histology with both H&E and modified Giemsa was considered as the reference standard. There were 33 males and the mean age (SD) of study subjects was 49.4(15.4) years. Endoscopically, forty-three (84.3%) patients had abnormal findings in the stomach predominated by prepyloric erosions (53.5%). Histologically, all patients had features of chronic gastritis and activity was detected in 94.1% of patients. Histologically (both H&E and modified Giemsa) 82.4% of patients had morphological evidence of H. pylori in the gastric mucosa. Stool antigen test was positive only in 7 out of 51 (13.7%) patients. The sensitivity and specificity of the stool antigen test in this study were 11.9% and 77.8%, respectively. The negative and positive predictive values were 15.9% and 71.4%, respectively. A low concentration of H. pylori stool antigen below the required level of detection could be a plausible explanation for false negative results. Furthermore, decreased shedding of the organism with increasing chronicity of infection may be another reason. Infection of the local population with a hitherto unknown strain of H. pylori is worth considering. In conclusion, until further testing is done, the validity of amplified IDEIA HpSt AR monoclonal antibody test as H. pylori detection technique in the local population cannot be supported by our observations.