Macrocytic Anemias

Question 1

What is the definition of macrocytosis?

Answer 1

increased MCV (beyond normal or ABOVE their baseline)

remember that MCV has a huge normal range, so you need to compare it to a previous (it may look normal but still be macrocytic)

Question 2

What general things will make RBCs big?

Answer 2

artifact (sticking tgether)
immature red cells
too much membrane
too much hemoglobin
"stressed" red cell population

Question 3

So why would you have a large MCV in a patient who is hymolyzing?

Answer 3

because they will have a makred reticulocytosis that can drive up your MCV

Question 4

So what lab should you add on right away when you see a high MCV?

Answer 4

a retic count

because high retic counts will elevate the MCV

Question 5

If the person does have a high retic count, what two things do you consider?

Answer 5

do they have a reason to have high epo?

if not, order hemolysis labs

Question 6

What are the two acquired conditions that will cause RBC membranes to be too big?

Answer 6

basically things that cause an excess of unesterified cholesterol in circulation that the RBCs take up:

liver disease
hypothyroidism

Question 7

What will RBCs look like if they have too much membrane?

Answer 7

target cells

Question 8

Why can chronic lung disease with CO2 retention lead to a megaloblastic anemia?

Answer 8

you get increased red cell water due to the chronic hypercapnia (difficult to handle pH and fluid shifts)

Question 9

Why can megaloblastic anemia mimic findings of hemolysis?

Answer 9

Because their oversized red cell precursors and red cells can’t divide and just get destroyed in the bone marrow leading to elevated LDH, haptoglobin, indirect bilirubin, etc.

Question 10

What are the limitations of B12 measurements?

Answer 10

we have 7 yrs of B12 stored in the liver but any inflammatory process will falsely increase the measured B12 level (because we don’t measure it directly, we measure it based on its carrier - transcobalamin2 which is an acute phase reactant)

Question 11

So how do you check for a B12 deficiency if the screen is normal?

Answer 11

check serum homocystiene and methylmethionine levels

Question 12

What are the limtis of folate measurement?

Answer 12

we have 3 months worth stored in red cells, but serum levels may not reflect storage levels; thus red cell folate level is more reliable

[someone who is folate-deficiency will start reticing within 12 hours after folate suppl and then you check the folate and it shoots up because of the retic’s folate]

Question 13

What are some examples of diseases that will “stress” the red cell production by decreasing numbers of erythroid precursors in the bone marrow?

Answer 13

aplastic anemia
chronic hep C
some B-cell lymphomas

Question 14

So generally speaking, what lab tests and other evaluations do you to when you see an elevated MCV?

Answer 14

remember the Hg x 3 - Hct

Retic count

LFTs and TFTs

B12, folate

Blood smear/ biopsy?