Macrocytic Anemia Flashcards
What is macrocytic anemia?
Anemia with MCV > 100 um^3
What is the most common macrocytic anemia?
Megaloblastic anemia caused by folate or B12 deficiency
How are folate and Vit B12 associated with DNA precursors?
MethylTHF circulates in blood. Vit B12 acquires methyl so that THF can participate in DNA synthesis. MethylB12 transfers methyl to homocysteine to form methionine.
What condition does Vit B12 and/or folate deficiency result in? What are the details of this condition?
Megaloblastic anemia which is characterized by hypersegmented neutrophils (> 5 lobes) and megaloblastic change on rapidly dividing epithelial cells.
What are 3 “other” causes of macrocytic (non-megaloblastic) anemia?
Alcoholism, liver disease, drugs
From what source is folate acquired and where in the body is it absorbed?
Green vegetables and some fruits. Jejunum
Roughly how long does it take for folate deficiency to occur?
Months (relatively quickly)
Causes of folate deficiency
Poor diet (alcoholics, elderly), increased demand (pregnancy, cancer, hemolytic anemia), folate antagonists (methotrexate which inhibits DHFR)
Folate deficiency lab findings
Macrocytic RBCs and hypersegmented neutrophils, Glossitis (inflamed tongue), decreased serum folate, increase serum homocysteine, normal methylmalonic acid (B12 needed to convert MMA to succinyl-CoA)
What is the source of Vit B12? Describe its absorption.
Vit B12 complexed to animal-derived proteins (meat, eggs). Salivary enzymes liberate B12 which binds to R-binder and carried thru stomach. Pancreatic proteases cleave R-binder from. B12 binds to intrinsic factor (from gastric parietal cells) which is absorbed into the ileum.
Which is more common: B12 or folate deficiency?
Folate deficiency. You have hepatic stores of B12 that can last you several years
What is the most common cause of B12 deficiency?
Pernicious anemia. Body destroys gastric parietal cells and therefore cannot produce IF to bind B12.
What are 3 other causes of B12 deficiency?
Pancreatic insufficiency (can’t cleave R-binder), Damage to terminal ileum (Crohn disease or Diphyllobothrium latum [fish tapeworm]), dietary deficiency is rare except in vegans
Clinical findings of B12 deficiency
Macrocytic RBCs w/ hypersegmented neutrophils, Glossitis, Subacute combinded degeneration of spinal cord (methylmalonic acid build-up because no B12 available to convert MMA to succinyl-CoA) and therefore a loss of proprioception, vibratory sensation, and spastic paresis, decreased serum B12, increased serum homocysteine, increased methylmalonic acid
What lab finding would allow you to distinguish between folate and B12 deficiency macrocytic anemia?
Increased methylmalonic acid in B12 deficiency. B12 required to convert MMA to succinyl-CoA
