[The diagnostic validity of Helicobacter pylori stool antigen test in the pre- and post-eradication]

The efficacy of a new enzyme immunoassay designed to detect H. pylori antigens in stool (HpSA) was evaluated before and after the eradication therapy.

HpSA test was performed in 75 patients whose H. pylori status was defined on the basis of concordant results of the 13C-urea breath test (13C-UBT), rapid urease test and histology. Fifty-one H. pylori-positive patients were treated with a week regimen of triple therapy (amoxicillin 1.0 g b.d., clarithromycin 500 mg b.d., rabeprazole 10 mg b.d). Four weeks after the completion of therapy, previous tests including HpSA were repeated on 29 of 51 patients. Six weeks after the completion of therapy, HpSA test was repeated on 10 of 29 patients.

Before the eradication, the sensitivity, specificity, and accuracy of HpSA test was 80.4%, 95.2% and 84.7%, respectively. When the cut-off value of 0.12 was adopted on the basis of our receiver operation characteristics (ROC) curve, the sensitivity and specificity improved as 90.0% and 95.2%. Four weeks after the completion of therapy, the sensitivity, specificity and accuracy of HpSA test was 50.0%, 88.9% and 86.2%, respectively. In 3 patients, false positive results at 4th week were converted to true negative at 6 weeks.

The HpSA test is a useful diagnostic method for H. pylori in pre-eradication stage. The specificity of HpSA test in the post-eradication was similar to other studies. For the velue of HpSA test in the post-eradication period, further studies about the cut-off value and the guideline of optimal time after the eradication may be needed.