Mean Corpuscular Volume (MCV)

Mean corpuscular volume (MCV) is the average volume of red cells in a specimen. MCV is elevated or decreased in accordance with average red cell size; ie, low MCV indicates microcytic (small average RBC size), normal MCV indicates normocytic (normal average RBC size), and high MCV indicates macrocytic (large average RBC size).

The reference ranges for MCV are as follows ^[1] :

• Adult/elderly/child: 80-95 fL
• Newborn: 96-108 fL

Mean corpuscular volume (MCV) is the average volume of red cells. It can be directly measured by automated hematology analyzer, ^[2] or it can be calculated from hematocrit (Hct) and the red blood cell count (RBC) as follows: ^[3]

• MCV in fl = (Hct [in L/L]/RBC [in x10¹²/L]) x 1000

MCV, along with mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC), is a part of RBC indices (erythrocyte indices), which are measurements and/or calculations for determining the size, content, and hemoglobin concentration.

More recently, red cell distribution width (RDW) has also been included as a part of RBC indices. The indices are useful in the morphologic characterization of anemia. Among these parameters, MCV is the most useful value used to classify the type of anemia based on red cell morphology. ^[2] Of note, type of anemia can also be categorized based on bone marrow responses to anemia using reticulocyte count into hypoproliferative anemia (decreased red blood cell production) and hemolytic anemia (increased red blood cell destruction).

Main types of anemia classified based on red cell morphology and their common causes

The common causes of microcytic and hypochromic anemia (decreased MCV and MCH) are as follows: ^{[4, 5, 6]}

• Iron deficiency anemia

• Anemia of chronic disease

• Thalassemia

• Sideroblastic anemia

The common causes of macrocytic anemia (increased MCV) are as follows: ^[4]

• Folate deficiency anemia

• Vitamin B12 deficiency anemia

• Liver disease

• Hemolytic anemias

• Hypothyroidism

• Excessive alcohol intake

• Aplastic anemia

• Myelodysplastic syndrome

The common causes of normocytic and normochromic anemia (normal MCV) are as follows: ^[4]

• Anemia of chronic disease

• Acute blood loss

• Hemolytic anemia, such as autoimmune hemolytic anemia, hereditary spherocytosis, or nonspherocytic congenital hemolytic anemia (G6PD deficiency, other)

• Anemia of renal disease

• Aplastic anemia

Of note, when considering the causes of anemia, the guidelines above are helpful but have limitations. For example, hemolytic anemia and aplastic anemia can manifest as normochromic and normocytic anemia or macrocytic anemia; anemia of chronic disease can be normochromic and normocytic anemia or microcytic anemia; sideroblastic anemia can be microcytic anemia, macrocytic anemia, or normochromic and normocytic anemia (due to the presence of dimorphic population of microcytes and macrocytes).

In addition, once the causes of anemia are considered, correlation with clinical findings, including history and physical examination, is important, as is, when necessary, performing more definitive tests to arrive with a definitive diagnosis.

Collection and panel details are as follows:

• Specimen: Whole blood, usually collected by venipuncture

• Collection: EDTA tube (purple/lavender top) containing EDTA potassium salt additive as an anticoagulant (see image below)

  EDTA tubes, purple top.

• Panels: Complete blood count (CBC)

Description

Mean corpuscular volume (MCV) is the average volume of red cells in a specimen. MCV is elevated or decreased in accordance with average red cell size; ie, low MCV indicates microcytic (small average RBC size), normal MCV indicates normocytic (normal average RBC size), and high MCV indicates macrocytic (large average RBC size).

Indications/Applications

Mean corpuscular volume (MCV) laboratory test, as part of a standard complete blood count (CBC), is used along with other RBC indices (MCH and MCHC) to help classify the cause of anemia based on red cell morphology. See also the Interpretation section above.

Considerations

MCV, as well as MCH and MCHC, reflect average values and may not adequately reflect RBC changes where mixed RBC populations are present, such as dimorphic RBC populations in sideroblastic anemia or combined iron deficiency anemia (decreased MCV and MCH) and megaloblastic anemia (increased MCV).

Elevated red cell distribution width (RDW) provides a clue for heterogenous red cell size (anisocytosis) and/or the presence of 2 red cell populations, and peripheral blood smear review can help confirm the above findings. ^{[7, 4]}

Of note, a third of older patients may have an elevated MCV without an identifiable cause. ^[2]

MCV can be falsely elevated in the presence of red blood cell agglutination (as in cold agglutinin disease or paraproteinemia) or severe hyperglycemia (glucose > 600mg/dL) as red blood cells become swollen. ^[7]