Macrocytic Anemias Flashcards
define macrocytosis
increase in MCV relative to a patient’s baseline
- Don’t forget! Normal range for MCV is AGE DEPENDENT
- Don’t forget! There is a broad normal range for MCV - Use your database (when available) to see what is normal for your patient
- Don’t forget! MCV changes only gradually for any given individual; a rapid change could indicate laboratory ERROR
What makes red cells big?
- Artifact (sticking together!)
- Immature red cells
- Too much membrane
- Too much stuffing
- Stressed red cell production
How do you figure out that a macrocytosis may be due to artifact?
Use the formula and call the lab!
How do immature cells cause macrocytosis?
– A young reticulocyte has an MCV of 140 fl
– The normal range for MCV in adults is 80-100 fl
– If you are hemolyzing and have a marked reticulocytosis you can, conceivably, drive up your MCV
Let s try it!
Let s say you have acute, or maybe even subacute, hemolysis with 20% reticulocytes and your baseline MCV is 95 fl.
– 0.2 X 140 fl + 0.8 X 95 fl = 104 fl
Obviously 20% is a very high reticulocyte count but it is worth being aware that a marked reticulocytosis (which is very frequently accompanied by folate deficiency) can give you a slight macrocytosis
19 year old male college student with sore throat and fatigue RBC L Hgb 10.9 L Hct 31% L Formula: 1.7 MCV 101 MACRO RDW 18 --> Retic! MCHC 35 N
Reticulocytes 25% HIGH
Macrocytic anemia with elevated reticulocyte count….eventually found to have EBV
If MCV is slightly elevated what is the first thing you shoiuld check?
reticulocyte count! (REMEMBER, this may be already available with the CBC you ordered and you just need to call and request that it be reported in the computer!)
If reticulocyte count is ELEVATED think…
– Is this patient on erythropoietin or somehow producing excess
erythropoietin?
– If not, it is time to order HEMOLYSIS LABS (which may
include a blood smear review - tomorrow s lecture)
What causes too much membrane that makes RBC big?
• When there is excess unesterified cholesterol in the circulation, this cholesterol is taken up by the red cell membrane making the cells larger - typically a mild increase in MCV
What are the 2 acquired conditions that can lead to increased levels of circulating unesterified cholesterol?
liver disease
hypothyroidism
If the MCV is only mildly elevated and the absolute/corrected retic count is LOw/normal think…
– Could this person have liver disease or be hypothyroid?
– Liver and/or thyroid function tests
Too much membrane leads to ____ shaped cells
target shaped!
what is megaloblastosis?
too much stuffing
– Vast majority of too much stuffing in red cells can be placed in the general category of megaloblastosis
– An unusual cause of too much stuffing is increased red cell water that can be seen with chronic hypercapnia (lung disease with CO2 retention)
– This is ALSO a general term for situations where you can make PROTEIN but you can t make DNA
– This means that the cells can get bigger and bigger (as long as there is a nucleus) but they can’t divide
Under what circumstances can nucleated cells make protein but not DNA causing megaloblastosis?
– Vitamin B12 or folate deficiency
– Drugs that block DNA synthesis
– Drugs that inhibit vitamin B12 or folate utilization
– Congenital metabolic abnormalities • Lesch Nyhan syndrome
• Methylmalonic aciduria
• Homocysteinuria without methylmethioninuria
– Myelodysplastic syndromes (“pre-leukemia”) or myeloid leukemias that impair DNA synthesis
When someone is severely “megaloblastic” their oversized red cell precursors and red cells are destroyed in the bone marrow and other lab tests (LDH, haptoglobin, indirect bilirubin, etc) will mimic the findings of ….
HEMOLYSIS!!!
