Normalized real-time PCR for diagnosis of H. pylori infection

Objectives: There is increasing interest in the use of quantitative PCR (q-PCR) for diagnosis of H. pylori infection. However, the assay remains largely unstandardized, making comparison between studies unreliable. The objective of this study was to assess accuracy of a normalized q-PCR assay for diagnosis of the infection. Subjects and methods: Seventy-six fresh gastric biopsy specimens were collected from patients undergoing upper gastrointestinal tract endoscopy and examined by rapid urease test (RUT), culture, and a commercial TaqMan q-PCR assay targeting the ureA gene. Counts obtained from the latter assay were normalized to the human ACTB gene. A subject was considered to be infected if two or more assays were positive. Results: The detection rates were 42.1%, 52.6%, and 78.9% by culture, RUT and q-PCR, respectively. Bacterial density ranged 0.005 to 4800 bacteria per 100 human cells. Because q-PCR showed low initial specificity (45.7%), the cutoff value for the assay was recalculated as 1 bacterium per 100 human cells, using ROC curve analysis. Accordingly, the sensitivities and specificities were 79.5% and 97.3%, respectively, for culture; 94.9% and 91.9%, respectively, for RUT; and 94.9% and 94.6%, respectively, for q-PCR. By gold standard, 39 of the dyspeptic patients (51.3%) were found to be infected. Conclusions: With the identified cutoff value, the q-PCR assay diagnosed H. pylori infection with an accuracy slightly superior to that of RUT. However, the possibility that low counts detected only by q-PCR represent true infections warrants further investigation. Normalization of bacterial counts for standardization of q-PCR H. pylori assays is recommended.