normocytic anemia- why hasn't BM responded?

[sanj238]

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Why doesn't the bone marrow respond to normocytic anemia? If someone could explain why the MCV is within normal range for extravascular condition ( say Sickle Cell) or for intravascular disorder and for G6PD deficiency I'd appreciate it. I would assume that an anemic condition due to overall hemoglobin dysfunction would mean more reticulocytes being made. In other words, why isn't the MCV changing?

Thanks

 

[withrye]

Retics are slightly larger than mature rbcs, but even an elevated retic is only around 5%, so it's not gonna drag up the MCV a ton. Basically, it's not a sensitive enough measure.

 

[sanj238]

Hmm

I'm not sure I understand? in microcytic anemia the reticulocyte count is elevated. Reticulocytes are SMALLER than normal RBC- hence the MCV values are lower than 80.

Why would reticulocytes be larger? That makes no sense.

Anyway that still doesnt get to the bottom of why normocytic anemia takes place at all. what does it even mean? I assume it has to do with some sort of increased concentration within the RBC which manages to stay the same size. But I can't quite get it into a manageable concept that explains all the different normocytic disorders.

 

[sobored]

Why doesn't the bone marrow respond to normocytic anemia? If someone could explain why the MCV is within normal range for extravascular condition ( say Sickle Cell) or for intravascular disorder and for G6PD deficiency I'd appreciate it. I would assume that an anemic condition due to overall hemoglobin dysfunction would mean more reticulocytes being made. In other words, why isn't the MCV changing?

Thanks

MCV only refers to RBC size. Normocytic means MCV is ~80-100. Retics will help you determine whether the anemia is due to RBC hemolysis (retic > 3%), or due to BM underproduction (retic <1%).

 

[Wordead]

It's been awhile since I looked at this stuff, but I'll give it a shot:

What source are you looking at? AFAIK, there absolutely is an elevated retic count anytime there is hemolysis and your bone marrow is competent.

Also, I think you have a couple misconceptions -

1. Reticulocytes ARE larger than normal RBCs, as they are still nucleated and have all that crap from erythroid precursors. In contrast, RBCs are just bags of hemoglobin.

2. Microcytic anemia just means that the SIZE of your RBCs are smaller, due to lack of hemoglobin. It has pretty much nothing to do with reticulocytes.

3. Normocytic just means that the size of your RBCs are normal between 80-100, signifying that there is no block in hemoglobin synthesis. Instead, your problems are antibodies, complement, or toxins destroying your RBCs. Contrast this with microcytic (insufficient hemoglobin = try to divide = small RBCs) and macrocytic (lack of DNA precursors = can't divide = large RBCs).

Hope that helped.

 

[withrye]

The precursors to rbcs get progressively smaller from the hematopoetic stem cell down to the myeloblast down to the reticulocyte ending with the rbc. In microcytic anemia, there is a problem making enough hemoglobin so the cell divides an extra time to preserve roughly the same concentration, so the end rbcs are a little smaller than normal. In a macrocytic anemia, a lack of dna precursors prevents division on schedule, so the rest of the cell grows larger than usual in the meantime.

In normocytic anemia, there's no problem with Hb or dna precursors. Instead, the cells are being sequestered, destroyed, or underproduced. This means they have no problem being made in the right proportion, it's just that there aren't enough of them. A normocytic anemia just means not enough red blood cells.

 

[MLT2MT2DO]

1. Reticulocytes ARE larger than normal RBCs, as they are still nucleated and have all that crap from erythroid precursors. In contrast, RBCs are just bags of hemoglobin.


Hope that helped.

Reticulocytes are not nucleated, but do have "all that crap from erythroid precursors". Just don't want anyone to get confused.

 

[medpack87]

The precursors to rbcs get progressively smaller from the hematopoetic stem cell down to the myelin last down to the reticulocyte ending with the rbc. In microcytic anemia, there is a problem making enough hemoglobin so the cell divides an extra time to preserve roughly the same concentration, so the end rbcs are a little smaller than normal. In a macrocytic anemia, a lack of dna precursors prevents division on schedule, so the rest of the cell grows larger than usual in the meantime.

In normocytic anemia, there's no problem with Hb or dna precursors. Instead, the cells are being sequestered, destroyed, or underproduced. This means they have no problem being made in the right proportion, it's just that there aren't enough of them. A normocytic anemia just means not enough red blood cells.

This is a very good and simple explanation. Thanks.