Knowledge Check

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How is macrocytosis defined?

a
Mean cell volume (MCV) > 65 fL
b
MCV > 100 fL
c
MCHC > 38 g/dL
d
MCV > 80 fL
e
RDW > 16%

Sort the condition according to the typical mean cell volume:

Iron deficiency
MDS
Hydroxyurea
Alcohol
Hb EE
Inflammation
Hyperthyroidism
Reticulocytosis
Thalassemia
Liver disease
Hb CC
Hypothyroidism
MCV < 80 fL
MCV > 100 fL

Abbreviation: MDS, myelodysplastic syndrome

True or false: increased reticulocytes cause a reduction in the mean cell volume.

a
True
b
False
They may cause an increase in the MCV.

True or false: macrocytosis may occur in the absence of anemia.

a
True
b
False

Macrocytosis without anemia is called isolated macrocytosis:

Table showing the % of cases of macrocytosis that are associated with anemia (and by extension those without anemia). The PMID numbers refer to the original studies.

Isolated macrocytosis:

  • More common in those with:
    • Mean cell volume (MCV) < 110 fL
    • Alcoholism
    • Medication-associated macrocytosis
    • Unexplained macrocytosis
  • Less common in those with:
    • MCV > 110 fL
    • Vitamin B12 deficiency
    • Hemolytic anemia
    • Underlying none arrow disease
    • Liver disease

True of false: with careful investigation, the cause of macrocytosis can be determined in virtually every patient.

a
True
b
False
A significant proportion remain undiagnosed
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