Human plasma is directly bacteriocidal against Helicobacter pylori in vitro, potentially explaining the decreased detection of Helicobacter pylori during acute upper GI bleeding.

BACKGROUND: The rapid urease test is the preferred method for detection of H pylori in patients with uncomplicated ulcer disease undergoing EGD. However, the sensitivity of this test when performed during upper GI bleeding has been questioned. It has been suggested that false-negative results occur, resulting from buffering effects of blood. The direct effect of blood was evaluated on H pylori growth in ex vivo and in vitro systems.
METHODS: Antral biopsy specimens obtained from 100 consecutive patients undergoing EGD were cultured with and without autologous blood, and RUT results at 5, 15, and 30 minutes were compared. In addition, H pylori bacterial cultures of a virulent laboratory strain were incubated with blood or blood components from 5 patients who were H pylori positive and 5 who were H pylori negative. The effect of blood on H pylori growth was determined by rapid urease test and direct bacterial plating with colony-forming unit determination.
RESULTS: Three hundred antral biopsy specimens from 100 patients were divided into 900 fragments for rapid urease test evaluation. There was no statistical difference in rapid urease test results for biopsy fragments tested immediately, cultured in blood, or cultured in phosphate-buffered saline solution. In contrast, in vitro studies demonstrated that whole blood and plasma effectively killed H pylori, whereas neutrophils and mononuclear cells had no detrimental effect on H pylori growth.
CONCLUSION: Human plasma contains factors that kill H pylori in vitro. This may be a possible explanation for the lower-than-expected rapid urease test detection of H pylori during active upper GI bleeding.