Serum Concentrations of Gastric Intrinsic Factor—A Pilot Study on Patients Undergoing Bariatric Surgery, Presenting with Portal Hypertension, or Suspected Pernicious Anemia

Background/Objectives: Small quantities of gastric parietal cell-derived Intrinsic Factor (IF) are present in circulation. Here, we explore circulating concentrations of IF in different medical conditions affecting the stomach, anticipating finding both low and high concentrations depending on the state of the parietal cells. Methods: We measured serum IF in (I) patients before and after bariatric surgery; (II) patients diagnosed with portal hypertension; and (III) patients with suspected pernicious anemia referred for measurement of IF autoantibodies. Results: Patients undergoing bariatric surgery (n = 25) showed a significant drop in serum IF following surgery. Their median serum IF declined from 5.1 pmol/L (pre-surgery) to 3.3 pmol/L (two months post-surgery), and nine out of 25 patients showed serum IF concentrations below reference interval (1.7–11.6 pmol/L). Most patients with portal hypertension (n = 18) showed normal serum IF concentrations, but with unexpectedly high concentrations up to 30 pmol/L in a few patients. Out of 120 patients referred for measurement of IF autoantibodies, 10 patients showed IF concentrations below the reference interval. Three out of four patients with IF autoantibodies showed low concentrations of circulating IF. Conclusions: Our study shows a decline in circulating IF following bariatric surgery consistent with the known decline in vitamin B12 uptake in these patients. Both high and low concentrations were observed in the other two groups. Future longitudinal studies are needed to illuminate possible usefulness for measurement of circulating IF.