Background: The 13C-urea breath test (13C-UBT) is a very accurate method of Helicobacter pylori diagnosis with a false-negative rate of 1-3%. However, the accuracy of the 13C-UBT is affected by potent acid inhibition with proton-pump inhibitors, which may suppress H. pylori and cause false-negative results. It is not known whether this occurs with less potent acid inhibition by H2-antagonists and any effect may be important clinically.
Objective: To determine the kinetics of 13CO2 excretion in H. pylori infected subjects during and after short-term ranitidine use.
Methods: Volunteers underwent a baseline 13C-UBT (positive: delta13CO2 > or = 5.0; negative: < or = 3.5; indeterminate: > 3.5 to < 5.0). Infected subjects took ranitidine 300 mg each evening for up to 28 days. 13C-UBTs were performed at weekly intervals and then every other day after ranitidine was ceased. If the 13C-UBT remained positive after 14 days, ranitidine was continued for a further 14 days.
Results: Thirty-one subjects were studied (mean age 40.4 +/- 2.1 years; 23 female/8 male; mean baseline delta13CO2 27.3 +/- 2.5). In 28 subjects the 13C-UBT remained positive during ranitidine use. The mean delta13CO2 rose to 124% (P< 0.06) and 121% (P < 0.05) of baseline at 14 and 28 days respectively. In two subjects, the delta13CO2 became indeterminate at day 7 (delta13CO2 4.3 and 3.8). In one of these, return to a positive value (delta13CO2 13.6; 103% of baseline) occurred while still on ranitidine. The other subject became positive again by day 3 off ranitidine (17.8; 119% of baseline). One subject had a transiently negative test after 21 days and this became positive again while still taking ranitidine.
Conclusions: Ranitidine has a minimal effect on the 13C-UBT. The rate of indeterminate or false-negative tests is no greater than in patients on no anti-secretory medication.