A new semiquantitative method of quantifying Helicobacter pylori in antigen stools

Stool antigen test for Helicobacter pylori, a noninvasive assay, is emerging as a strong competitor to urea breath test (UBT). Nevertheless, although the UBT delta value is a semiquantitative indicator of H. pylori intragastric load, until now the H. pylori stool antigen test has been used only as a qualitative investigation. We report here the results of a study performed with the aim of obtaining a semiquantitative measurement of bacterial amount in stools. We studied 15 patients with dyspepsia using H. pylori positivity at histology, the rapid urease test, UBT, and the H. pylori stool antigen test. The result of this last test was expressed by a numerical value we obtained by applying the principle of "standard points" to the absorbance units at spectrophotometric reading. This measurement was previously validated by testing probe sampling of H. pylori stool antigen with known pure and stool-mixed bacterial amounts. A numerical result for H. pylori stool antigen was correlated to UBT delta for each patient using Pearson's r test. Finally, a Student t test was performed to investigate possible differences in UBT and H. pylori stool antigen test values between anti-CagA-positive and -negative patients. We obtained a curve of saturation with both known amount of pure and stool-mixed bacteria. Pearson's r test showed a significant correlation between UBT delta value and H. pylori stool antigen measurement (r = 0.77; p < 0.001). Urea breath test delta and H. pylori stool antigen test values were significantly higher in anti-CagA-positive patients. Our data suggest that a numerical estimation of H. pylori stool antigen may be feasible. This evaluation, similarly to UBT delta, may represent a semiquantitative determination of bacterial intragastric load.