MCV - 42fL
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
An MCV of 42 fL is severely microcytic — far below the normal range.
Interpretation of MCV = 42 fL
Normal Range
The normal MCV is 80–100 fL (some sources cite 85–95 fL). — Harrison's Principles of Internal Medicine 22E, Table 66-1
Classification
| MCV | Classification |
|---|---|
| < 80 fL | Microcytic |
| 80–100 fL | Normocytic |
| > 100 fL | Macrocytic |
An MCV of 42 fL is severely microcytic (normal lower limit is ~80 fL, so this is roughly half the lower bound of normal).
What Causes Such a Low MCV?
Microcytic anemias reflect a quantitative defect in hemoglobin synthesis. The major causes, in order of likelihood with a very low MCV like 42 fL, are:
| Cause | Typical MCV | Notes |
|---|---|---|
| β-Thalassemia major/intermedia | 55–65 fL | Lowest MCVs; striking microcytosis |
| α-Thalassemia | 65–75 fL | Moderate microcytosis |
| Severe iron deficiency anemia | Can fall <60 fL in chronic/severe cases | Most common cause overall |
| Hemoglobin E disease | Very low | Common in SE Asia |
| Sideroblastic anemia | Variable, can be very low | Lead poisoning, pyridoxine deficiency |
| Anemia of chronic inflammation | Rarely <75 fL | Usually mild microcytosis only |
An MCV of 42 fL specifically suggests thalassemia (especially β-thalassemia) or a combined defect (e.g., thalassemia + iron deficiency). Anemia of chronic disease alone would not produce such a low MCV. — Goldman-Cecil Medicine: "An MCV less than 75 fL would not be seen in the anemia of inflammation."
Next Steps
To identify the cause:
- Iron studies — serum iron, ferritin, TIBC, transferrin saturation
- RDW — elevated in iron deficiency; normal/mildly elevated in thalassemia trait
- Peripheral blood smear — target cells, hypochromia, poikilocytosis
- Hemoglobin electrophoresis / HPLC — to detect HbA2 elevation (β-thalassemia), HbF, HbH, HbE
- Reticulocyte count
— Tietz Textbook of Laboratory Medicine, 7th Ed.; Henry's Clinical Diagnosis and Management by Laboratory Methods
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