13. Hematology Flashcards
What is the purpose of B12?
Takes the methyl group of tetrahydrofolate; THF can’t help make DNA if it’s methylated
What does B12 do with the methyl group from THF?
Gives it to homocysteine to make methionine
What is the serum homocysteine level in B12/folate deficiency?
High
What is the most common cause of elevated homocysteine?
Folate deficiency
What does increase in homocysteine levels put you at risk for?
Thrombocytosis and MI
What is a specific test for B12 deficiency?
Elevated methylmalonic acid because B12 is a cofactor for the conversion of methylmalonyl coA to succinyl coA
What is the purpose of R factor?
Protects B12 from being destroyed in the stomach; binds in saliva
What makes intrinsic factor?
Parietal cells
Where is B12-IF complex absorbed?
Terminal ileum
Where is folate absorbed?
Jejunum and ileum
What drug causes folate deficiency because it inhibits intestinal conjugase?
Phenytoin
Why are alcoholics at increased risk of folate deficiency?
Alcohol blocks absorption of folate
What is the hallmark histology for B12 and folate deficiency megaloblastic anemias?
Hypersegmented neutrophils
How do we differentiate between B12 and folate deficiency?
Neuro exam - neurological deficits in B12 deficiency
What are the 3 causes of B12 deficiency that we can check with a Schilling test?
- Pernicious anemia - get radiolabeled B12 when we give with intrinsic factor
- Bacterial overgrowth - get radiolabeled B12 when we give antibiotics
- Pancreatitis - get radiolabeled B12 when we give pancreatic enzymes
