non-megaloblastic macrocytic anemia

[Aclamity]

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This little portion in FA confuses me... it says that these are "Macrocytic anemia in which DNA synthesis is unimpaired," but then gives examples of 5-FU, AZT, hydroxyurea, and congenital deficiencies of purine/pyrimidine synthesis. Aren't these going to cause impairment of DNA synthesis?

Also, what do they mean by "reticulocytosis --> inc MCV"?? Does that mean conditions causing massive reticulocytosis (like chronic hemolysis) will result in non-megaloblastic macrocytic anemia? What would be the mechanism for this?

 

[lemonade90]

Not sure about the first part.

But from what I remember reticulocytes are slightly larger than normal RBCs so MCV should go up.

 

[beeitchness]

anyone else have an answer to this?

 

[Kaputt]

This little portion in FA confuses me... it says that these are "Macrocytic anemia in which DNA synthesis is unimpaired," but then gives examples of 5-FU, AZT, hydroxyurea, and congenital deficiencies of purine/pyrimidine synthesis. Aren't these going to cause impairment of DNA synthesis?

It's an error in FA. Any process where DNA synthesis is impaired (folate deficiency, B12 deficiency, orotic aciduria, AZT, 5-FU, etc) will be megaloblastic.

Alcohol can have a non-megaloblastic macrocytic anemia.

Also, what do they mean by "reticulocytosis --> inc MCV"?? Does that mean conditions causing massive reticulocytosis (like chronic hemolysis) will result in non-megaloblastic macrocytic anemia? What would be the mechanism for this?

I think, but someone correct me if I'm wrong, that reticulocytes are slightly bigger than "aged"/normal RBCs. Thus, if you've got a crap-ton of retics out there, your MCV will increase. But this is not a megaloblastic anemia because DNA synthesis isn't impaired.

 

[beeitchness]

It's an error in FA. Any process where DNA synthesis is impaired (folate deficiency, B12 deficiency, orotic aciduria, AZT, 5-FU, etc) will be megaloblastic.

Alcohol can have a non-megaloblastic macrocytic anemia.



I think, but someone correct me if I'm wrong, that reticulocytes are slightly bigger than "aged"/normal RBCs. Thus, if you've got a crap-ton of retics out there, your MCV will increase. But this is not a megaloblastic anemia because DNA synthesis isn't impaired.

Thanks. So it's a pretty glaring error that they still haven't put in the errata..

 

[Kaputt]

Thanks. So it's a pretty glaring error that they still haven't put in the errata..

They partially addressed it in their recent errata. If you read in different sections, you'll find it inconsistent. Orotic aciduria and antimetabolites all say "megaloblastic" in their own sections. It's just the page with all the macrocytic anemias in the heme/onc chapter that is screwed up.

 

[Aclamity]

I think, but someone correct me if I'm wrong, that reticulocytes are slightly bigger than "aged"/normal RBCs. Thus, if you've got a crap-ton of retics out there, your MCV will increase. But this is not a megaloblastic anemia because DNA synthesis isn't impaired.

Yep, this is correct. Took me a while to finally realize that reticulocytes actually get counted in the MCV calculation, so basically if you have a s**tload of retics it'll throw off the average. If you look at each individual MATURE rbc it looks the same as a normal rbc

They partially addressed it in their recent errata. If you read in different sections, you'll find it inconsistent. Orotic aciduria and antimetabolites all say "megaloblastic" in their own sections. It's just the page with all the macrocytic anemias in the heme/onc chapter that is screwed up.

Correct again. So all the stuff I mentioned in my first post are indeed megaloblastic anemias. The "non-megaloblastic macrocytic anemias" really are simply EtOH and liver disease. Hope this helps. FA really dropped the ball on this little section.

 

[aspiringmd1015]

how do alcohol and liver disease cause macrocytic anemia??