Mean corpuscular volume

The mean corpuscular volume, or "mean cell volume" (MCV), is a measure of the average red blood cell volume that is reported as part of a standard complete blood count.

In patients with anemia, it is the MCV measurement that allows classification as either a microcytic anemia (MCV below normal range), normocytic anemia (MCV within normal range) or macrocytic anemia (MCV above normal range).

Methodology And Normal Values

• To calculate the MCV, expressed in femtoliters (fL, or 10^-15L), the following formula is used:10 x hematocrit (%) divided by RBC count (millions/mm³). The normal ranges using this method are as follows : 80-95 fL.^[1]
• Use of volume-sensitive automated blood cell counters, such as the Coulter counter. In this type of apparatus, the red cells pass one-by-one through a small aperture and generate a signal directly proportional to their volume.
• Other automated counters measure red blood cell volume by means of techniques that measure refracted, diffracted, or scattered light.^[2]

If the MCV was determined by automated equipment, the result can be compared to RBC morphology on a peripheral blood smear. Any deviation would be indicative of either faulty equipment or technician error.

For further specification, it can be used to calculate red blood cell distribution width (RDW).

Interpretation

The normal reference range is typically 80-100 fL.^[3]

High

In presence of hemolytic anaemia, presence of reticulocytes can increase MCV. In pernicious anemia (macrocytic), MCV can range up to 150 femtolitres. An elevated MCV is also associated with alcoholism^[4] (as are an elevated GGT and a ratio of AST:ALT of 2:1). Vitamin B12 and/or folic acid deficiency has also been associated with macrocytic anemia (high MCV numbers).

Low

The most common causes of microcytic anemia are iron deficiency (due to inadequate dietary intake, gastrointestinal blood loss, or menstrual blood loss), thalassemia, or chronic disease. In iron deficiency anemia (microcytic anemia), it can be as low as 60 to 70 femtolitres. In cases of thalassemia, the MCV may be low even though the patient is not iron deficient.

A low MCV number in a patient with a positive stool guaiac test (bloody stool) is highly suggestive of GI cancer.

Worked example

Measure	Units	Conventional units	Conversion
Hct	40%
Hb	100 grams/liter	10 grams/deciliter	(deci- is 10-1)
RBC	5E+12 cells/liter	5E+12 cells/liter
MCV = Hct / RBC	8E-14 liters/cell	80 femtoliters/cell	(femto- is 10-15)
MCH = Hb / RBC	2E-11 grams/cell	20 picograms/cell	(pico- is 10-12)
MCHC = Hb / HCT	250 grams/liter	25 grams/deciliter	(deci is 10-1)

References

1. ^ The McGill Physiology Virtual Lab (30 September 2011). "Blood cell indices > MCV and MCHC". McGill Faculty of Medicine. http://www.medicine.mcgill.ca/physio/vlab/bloodlab/mcv-mchc_n.htm. 
2. ^ Stanley L Schrier, MD Stephen A Landaw, MD, PhD (30 September 2011). "Mean corpuscular volume". uptodate.com. http://www.uptodate.com/contents/mean-corpuscular-volume. 
3. ^ MedlinePlus Medical Encyclopedia: RBC indices
4. ^ Tønnesen H, Hejberg L, Frobenius S, Andersen J (1986). "Erythrocyte mean cell volume--correlation to drinking pattern in heavy alcoholics". Acta Med Scand 219 (5): 515–8. doi:10.1111/j.0954-6820.1986.tb03348.x. PMID 3739755. 

See also

• Anemia: Differential Diagnosis
• Full blood count
• Mean corpuscular hemoglobin