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  #1  
Old 04-01-2012
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RBC Macrocytic versus Megaloblastic!

Guys, can anyone tell me the difference between the terms macrocytic and megaloblastic.
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  #2  
Old 04-01-2012
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And simply megaloblasts are RBCs in bone marrow smear whereas macrocytes in the peripheral blood. Folate and B12 defficiency cause megaloblastic-macrocytosis but macrocytes can form in peripheral blood without prior megaloblasts in the bone marrow (nonmegaloblastic macrocytosis) as can occur from alcoholic dammage of RBCs (not associated with lack of folate or B12)


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Last edited by MedicalExaminer; 04-01-2012 at 03:24 PM.
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Old 04-03-2012
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Megaloblastic anemia is also the only kind with hypersegmented neutrophils.
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  #4  
Old 02-02-2013
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Default macrocytic vs megaloblastic anemia

I was confused about this too. The answer is in the name: "blast" = immature precursor form.

Megaloblastic anemia: impairments in DNA synthesis (e.g. folate, B12 deficiency, orotic aciduria) result in abnormal development of the nucleated erythroblasts (RBC precursors) in the marrow. These precursor cells cant make DNA properly, so their division is delayed while cytoplasmic protein synthesis continues unhindered ("nuclear-cytoplasmic asynchrony"), so they swell up and look weird during replication, i.e. become megaloblasts (big erythroblasts, nice picture here). Eventually these big megaloblasts lose their nuclei and become big mature circulating RBCs, i.e. become macrocytes (big erythrocytes). The same DNA synthesis defect which impairs division of RBC precursors also impairs division of other marrow precursor cells, for example granulocyte precursors are affected resulting in hypersegmented neutrophils and possible low WBC counts, and platelet precursors affected, possibly leading to thrombocytopenia.

Technically, in order to make a diagnosis of megaloblastic anemia, a bone marrow biopsy would need to be performed in order to demonstrate megaloblasts in the marrow (although in practice this may not always be done as it is invasive). The MCV is only a measure of the size of circulating RBCs. MCV > 100 is macrocytosis by definition, but not necessarily megaloblastosis.

Macrocytosis can occur in a variety of settings and only a small minority of macrocytosis is due to megaloblastosis. I.e. a process can occur that causes mature RBCs to swell but (mostly) doesn't affect RBC production in the marrow. Alcohol abuse, liver disease, and various drugs (e.g. Sunitinib) are commonly cited examples but I had trouble finding a good source for a mechanism. Some random internet sources say the mechanism of macrocytosis in liver disease is disordered lipid metabolism causing excess lipid deposition in RBC membranes causing them to swell, but I couldn't find a great source for this. With regard to alcohol abuse, I believe the mechanism is not well known. Elevated MCV can occur in reactive polycythemia because reticulocytes are larger than erythrocytes.

In summary, macrocytosis refers only to elevated MCV; it is common, and can be due to a variety of mechanisms and processes some of which are not well understood. Megaloblastosis refers to macrocytosis due specifically to impaired DNA synthesis leading to nuclear/cytoplasm asynchrony in RBC precursors manifesting as megaloblasts on marrow biopsy and macrocytes and hypersegmented neutrophils on peripheral smear. Megaloblastosis is usually due to B12 and/or folate deficiency.

Hope this helps!
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Old 04-18-2014
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Hi, I'm resurrecting this because I just wanted to get things clear in my head -

We have the megaloblastic, which refers to RBCs in the marrow and which can also produce hypersegmented neutrophils dependant on the cause.
We have the macrocytic which refers to RBCs in the peripheral blood

Then we have microcytic which refers to a reduction of hemaglobin within the peripheral blood RBCs?

So what does the term anemia specifically define? All of the above? Are they all anemias?
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Old 04-20-2014
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Quote:
Originally Posted by Kelly17 View Post
Hi, I'm resurrecting this because I just wanted to get things clear in my head -

We have the megaloblastic, which refers to RBCs in the marrow and which can also produce hypersegmented neutrophils dependant on the cause.
We have the macrocytic which refers to RBCs in the peripheral blood

Then we have microcytic which refers to a reduction of hemaglobin within the peripheral blood RBCs?

So what does the term anemia specifically define? All of the above? Are they all anemias?
Yes all are anemias, anemia= reduction in circulating RBC mass. [based on MCV classified into normocytic, micro, macro]

megaloblastic anemia: due to folate or vit b12 defic, impairs synthesis of DNA precursors, which will affect RBC, granulocytes, & rapidly dividing epithelial cells.
macrocytic anemia: affect RBCs only!
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  #7  
Old 04-20-2014
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Thanks very much for clearing that up.

Next question:
If you have a macrocytic anemia ie a b12 and a corresponding microcytic anemia ie iron, how could that skew the blood test results? (without doing a specific b12 and iron test)
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Old 04-21-2014
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Quote:
Originally Posted by Kelly17 View Post
Thanks very much for clearing that up.

Next question:
If you have a macrocytic anemia ie a b12 and a corresponding microcytic anemia ie iron, how could that skew the blood test results? (without doing a specific b12 and iron test)

Again Based On MCV
Normocytic - 80-100
Microcytic - < 80
Macrocytic - > 100

Hope this helps you
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Old 04-21-2014
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Thanks, but I don't think I'm quite there - maybe I didn't make my point well enough.

I have some guidelines here from a hematological body and they say that if you have a b12 deficiency and an iron deficiency both at the same time, one will mask the other, so what you end up with is normal MCV and a normal blood count - even though you have 2 separate deficiences.
I'm not questioning the fact that the one can mask the other but I do wonder exactly how it masks it in hematological terms?
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Old 04-21-2014
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In combined b12 and iron def, the MCV will be normal, but the Hb will be low and the peripheral smear will show both macrocytes and microcytes.
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Old 04-21-2014
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I'm not trying to be difficult, just trying to understand it - this is what I've got:

"Vitamin deficiency (b12) may be present without macrocytosis particularly when there is a concomitant iron deficiency or thalassaemia trait. There may be a dimorphic red cell population and macrocytosis may only become manifest when iron deficiency has been corrected. Neutrophil hypersegmentation is not specific...In addition it is not present in every patient with vitamin deficiency (which we've covered), its absence is especially to be noted in patients who are seriously ill and neutropenic."
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Old 05-01-2014
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Quote:
Originally Posted by Kelly17 View Post
I'm not trying to be difficult, just trying to understand it - this is what I've got:

"Vitamin deficiency (b12) may be present without macrocytosis particularly when there is a concomitant iron deficiency or thalassaemia trait. There may be a dimorphic red cell population and macrocytosis may only become manifest when iron deficiency has been corrected. Neutrophil hypersegmentation is not specific...In addition it is not present in every patient with vitamin deficiency (which we've covered), its absence is especially to be noted in patients who are seriously ill and neutropenic."
my friend i think youre crossing over way too far from step1 concepts.
good to clear things up but not quite relevant for step1 IMO.
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Old 05-01-2014
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Do you think it would be more beneficial to start a new thread?
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Old 05-02-2014
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Quote:
Originally Posted by Kelly17 View Post
Do you think it would be more beneficial to start a new thread?
lol. probably
you cracked me up with the "resurrecting" part.
good luck.
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Old 12-08-2014
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Let me take a stab at it :

Megaloblastic anemia =

1. RBC w/ MCV >100
2. hypersegmented neutrophil (w/5 or more lobes)
3.megaloblastic change in intestinal epithelial cell (ie all rapidly dividing cells).
4. due to b12/ due to folate as cause or secondary causes leading to low b12/folate such as:

i) auto immune reactions against parietal cell ( type2 hypersens rxn pernicious anemia)
ii) auto immune response against IF ---someone check this?
iii) lack of pancreatic enzymes to cleave off (r-factor and add intrinsic factor to b12).
iv) gut bacteria eating b12 --solved by antibiotics.
v)chrons disease /celiac / diverticulum /resection of the distal ileum 80cm.
etc.

NON-Megaloblastic (macrocytic) anemia =

1. rbc w/ MCV >100 or near 100.
2. NO hypersegmented neutrophil, or < 5 lobes on the nuetrophil.
3. NO megaloblastic in rapidly divinding intestinal cells.
4.non b12/folate causes IE:

i) alcoholism
ii) liver disease
iii) 5-Flourouracil.

Hope this helps :-) .
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Old 12-10-2014
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hi an interesting fact i came to know recently , vit C defficiency can cause both microcytic anemia ( as it is required for iron absorption fe+++ to fe ++ form )

and macrocytic megaloblastic anemia ( as its required for keeping the THF in its reduced form ) :P
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Old 02-07-2015
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I just finished hemo/onco rotation and saw a case with exactly that: IDA and megalobastic anemia. The result of the two is that you will see normal MCV but ELEVATED RDW. This is because MCV is an average of all the RBC size. However, RDw will be elevated because there exist a spectrum of cells that are macrocytic and microcytic. Great question thought. Interpreting CBC is really an art more than a science. So in sum, on CBC you will see anemia, normal MCV but if you look at RDW it will elevated. Then you look at the blood smear and you will see hypersegmentation of neutrophil, then you will also do an iron study as it is the most common cause of microcytic anemia.
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