Detection of malabsorption of vitamin B12 due to gastric or intestinal dysfunction

Abstract

In vivo tests for detection of vitamin B 12 malabsorption involve feeding 0.5–2 μ g of the vitamin, labeled with 56 Co (half-life, 77 days), 57 Co (half-life, 270 days), 58 Co (half-life, 71 days), or 60 Co (half-life. 5.26 yr), and measuring the amount absorbed by the amount of radioactivity in either stool, urine, blood, liver, or whole body. The test is divided into three stages: (1) Feed radio B 12 alone. Subnormal absorption ‘means. gastric or ileal dys function. Need not be done if in vitro radioassay for intrinsic factor carried out. (2) Feed radio Biz plus intrinsic factor concentrate. Subnormal absorption means ileal dysfunction, but does not rule out concomitant gastric dysfunction. (3) Only done if second stage is subnormal. Feed antibiotic (or anthelminthic) for appropriate period, then feed radio B 12 . Normal result means patient had blind loop syndrome (or fish tapeworm). When pancreatic dysfunction is suspected, the third stage consists in feeding the radio-B 12 with added bicarbonate or pancreatin or both. When drug-induced B 12 malabsorption is suspected, the third-stage test is the test after withdrawal of the offending agent. In vitro radioassay tests for B 12 malabsorption include: (1) Serum B 12 level: subnormal levels nearly always mean inadequate ingestion or absorption of B 12 . (2) Gastric intrinsic factor: lack means inability to absorb B 12 due to gastric dysfunction. (3) Circulating antibody to intrinsic factor: presence means the same as lack of gastric intrinsic factor; present in about two-thirds of patients who lack intrinsic factor. (4) Radioassay of ileal biopsy: a research test for functionality of the ileal receptor mechanism for intrinsic factor-mediated B 12 absorption. Every patient with B 12 malabsorption that is not unequivocally of a single cause should be retested after therapy to separate primary from secondary malabsorption.