macrocytosis

[aspiringmd1015]

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how do the causes of macrocytosis, not cause hypersegmentation etc, or simply whats the difference b/w macrocytosis and meg anemia?

 

[aspiringmd1015]

anyone?

 

[RnaPolymerase2]

Macrocytosis is MCV greater than a 100. while megaloblast has impaired DNA synthesis issue. Any thoughts?

 

[EmetyreUSMLEStep1Tutor1]

how do the causes of macrocytosis, not cause hypersegmentation etc, or simply whats the difference b/w macrocytosis and meg anemia?

Megaloblasts in the bone marrow. In liver disease/alcohol abuse/hypothyroidism there will be macrocytes(MCV>100) in blood, but there will be not megaloblasts in BM

 

[aspiringmd1015]

agreed, but why do those d/o's cause an eleated MCV?

 

[PaxRoma]

I think of it in plain and simple terms
Macrocytosis just means many big cells
Megaloblastic anemia however, is a disease diagnosis, which can include lab finding of macrocytosis, among other clinical findings.
A mature blood cell is smaller in size than an immature blood cell. Elevated MCV means the cells fail to divide another cycle to reach maturity due to lack of materials (DNA building blocks, etc).

 

[aspiringmd1015]

thats obvious, and so are the causes of all the cases of macrocytosis, im asking for the mechanism here.

 

[Transposony]

Macrocytosis means that RBCs that are larger than normal i.e. MCV > 100 fL.
There are several causes, one of them being megaloblastic anemia - a DNA synthesis defect.
For example, reticulocytosis is one of the cause of macrocytosis among others like COPD (too much Co2 --> too much water in the RBCs) and splenectomy, liver disease (too much membrane lipids) etc
Nuclear defects (e.g. hypersegmentation) happens because the nucleus is not yet ready to divide (as it's rate of maturation is slowed as compared to the rest of the cell).
So the "mega" cell is actually "stuck" in the "blast" like state as it is unable to divide (cytoplasm is ready to divide but the nucleus is not).
Therefore you end up with one big cell with hypersegmented nucleus where it should have been two normal cells.

 

[aspiringmd1015]

I understand the pathogenesis of megaloblastic anemia, thats clear, don't understand the other causes of just macroctysis.