Losing weight plus vitamin B12 following semaglutide administration? A case of false B12 deficiency

Abstract

Abstract Semaglutide is increasingly used to lose weight. We describe a case of an obese woman with unremarkable medical history. Following semaglutide administration, she managed to lose 10 kg over a period of 8 months, but B12 levels were markedly decreased. She had a series of previous annual tests including B12 results during routine check-up, which were performed in the same laboratory of the university hospital of Ioannina in Greece and consistently found normal B12 levels. She is not vegetarian, she had no symptoms or signs related to macrocytosis, anemia or B12 deficiency, blood smear examination did not reveal macro-ovalocytes, tear-drop cells, polychromatophilia, or hyper-segmented neutrophils, and the reticulocyte, white blood cell and platelet counts were within the normal range. We additionally measured homocysteine and methylmalonic acid which were within the normal range, whereas the antibodies against intrinsic factor were also negative. B12 levels are commonly measured using competitive binding immunoenzymatic assay. We postulate that for assays employing antibodies, a possibility exists for interference by heterophile antibodies boosted by semaglutide. Importantly, in diabetic patients semaglutide follows the introduction of metformin, which is frequently associated with low B12 levels, and in those cases, we tend to attribute low B12 levels only to metformin.