Macrocytic anemia is defined by a mean corpuscular volume (MCV) >100 fL. In simple terms, this means the red blood cells are larger than normal. The most common causes of macrocytic anemia are alcoholism, vitamin B12 and folate deficiencies, and medications. Vitamin B12 (cobalamin) is a water-soluble vitamin commonly found in fish, meat, and dairy products which is involved in neurologic function, red blood cell production, and as a cofactor for enzymes involved in DNA synthesis and metabolic function. Folate (Vitamin B9) is involved as a cofactor for many enzymes involved in DNA synthesis and metabolic function similar to vitamin B12
Lack or Impairment of Absorption
Normal physiology: Vitamin B12 is dissociated from food proteins by gastric acid and is then absorbed in the small intestine by binding with intrinsic factor which is secreted by parietal cells in the stomach
Folate Deficiency (Vitamin B9)
Peripheral Blood Smear
Additional Testing for Megaloblastic Anemia with High Suspicion for Vitamin B12/Folate Deficiency
Note: Serum folate level fluctuates rapidly with dietary intake and are thus not useful in determining folate stores and folate deficiency
Non-Megaloblastic Process or Negative B12/Folate Deficiency
Note: Guidelines recommend 1mg of oral vitamin B12 daily in gastric surgery patients due to the high risk and prevalence of vitamin B12 deficiency in this population
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