Vitamin B 12 Deficiency

General Information
  • Cobalamin is necessary for DNA synthesis and is found in sardines, shrimp, calf’s liver, and other animal meats.
  • Cobalamin is released from food by gastric peptidases and is then absorbed in the ileum through intrinsic factor.
  • Because of the large hepatic reservoir and efficient reuptake by the enterohepatic system, cobalamin deficiency due to decreased PO intake takes several years to develop.
 Etiology
  • Malabsorption – pernicious anemia, inflammatory bowel disease, celiac disease, bacterial overgrowth, pancreatic insufficiency
  • Pernicous anemia is due to antibodies directed at hydrogen potassium adenosine triphosphatase in the parietal cell membrane causing parietal cell atrophy and reduced intrinsic factor levels
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Clinical Presentation
  • Glossitis, weight loss, pale yellow skin, abdominal pain secondary to gastritis
  • Loss of vibration and propioception which can progress to spastic ataxia, hallucinations, dementia, psychosis
Diagnosis
  • Peripheral smear can show hypersegmented neutrophils, basophilic stippling, oval macrocytes
  • Hemolysis, thrombocytopenia, and leukopenia are other common lab findings due to inefficient hematopoiesis
  • Elevated homocysteine and methylmalonic levels; high methylmalonic levels are more sensitive and specific in diagnosing cobalamin deficiency than actual cobalamin levels
Treatment
  • Parental: 1000mcg daily for 1 week, 1000mcg once a week for 4 weeks, 1000mcg every month for rest of life
  • Oral: 1000mcg-2000mcg PO every day. Recent research has shown PO regimens to be comparable to parental as it is thought that the presence of a second, lower efficiency transport system for cobalamin which does not require intrinsic factor or a functioning terminal ileum can be utilized