Does fasting serum gastrin predict gastric acid suppression in patients on proton-pump inhibitors?

Proton pump inhibitors (PPIs) block gastric acid secretion and may increase serum gastrin concentration. The aim of this study was to determine whether fasting serum gastrin concentration predicts gastric acid suppression in patients on PPI therapy. Ambulatory pH monitoring with one pH probe in the distal esophagus and a second probe in the stomach was performed in patients with persistent symptoms of GERD despite PPI treatment. Upon completion of pH monitoring, blood was drawn for measurement of fasting serum gastrin concentration. In all, 51 patients were studied: 26 on PPIs, 1 on H2-receptor antagonists, and 24 off acid suppression. Fasting serum gastrin correlated inversely with percent time of gastric pH < 4 for all patients (r = -0.553; P<0.001) and for the subgroup of 26 patients on PPIs (r = -0.435; P = 0.027). In patients on PPIs, an elevated gastrin (> or =100 pg/ml) was associated with gastric pH < 4 for 25+/-7% of the time compared to 54+/-5% when the gastrin was normal (P = 0.004). Therapeutic gastric acid suppression (gastric pH < 4 for <50% of time) was present in 6 of 7 (86%) patients with an elevated fasting serum gastrin, compared with only 8 of 19 (42%) patients with a normal serum gastrin (P<0.05). In conclusion, there is a significant inverse correlation between the fasting serum gastrin concentration and gastric acid profile in patients with GERD. An elevated fasting serum gastrin concentration while on PPI therapy suggests that gastric acid secretion is adequately suppressed.