RBC indices
1. Mean corpuscular volume (MCV)
a. Definition: The MCV is the average volume of the RBCs.
b. Frequently used to classify anemia into a:
(1) microcytic anemia: MCV <80 µm3.
(2) normocytic anemia: MCV 80–100 µm3.
(3) macrocytic anemia: MCV >100 µm3.
2. Mean corpuscular Hb concentration (MCHC)
a. Definition: MCHC is the average Hb concentration in RBCs.
b. Clinical significance of a decreased MCHC
(1) Correlates with decreased RBC synthesis of Hb (e.g., iron deficiency anemia)
(2) Recognized by noting that the central area of pallor in a RBC is greater than normal
because there is less Hb in the cell
• This is called hypochromasia
c. Significance of an increased mean corpuscular Hb concentration
(1) Correlates with the presence of spherical RBCs, which occurs in hereditary spherocytosis (HS)
• Mature RBCs are biconcave disks (discussed later).
(2) Spherocytes lack the central area of pallor that is present in a mature RBC.
3. RDW
a. Definition: RDW is a measure of the variation in the size of the peripheral blood RBCs (i.e., small ones, big ones).
(1) Size variation is called anisocytosis.
(2) RDW value is only clinically significant if it is increased.
b. RDW is increased if RBCs are not uniformly the same size.
• Example: peripheral blood shows a mixture of microcytic and normocytic cells
c. RDW is most useful in distinguishing iron deficiency from other causes of a microcytic anemia (small RBCs).
(1) Iron deficiency is the most common microcytic anemia with an increased RDW.
• RDW is increased because of a mixture of normocytic and microcytic RBCs in the peripheral blood.