RBC Count

Here we are focusing on the RBC count. The RBC count in this patient is written as 4.36, which indicates:

• 4.36 x 10¹²/L
• 4.36 x 10⁶/ul
• 4.36 x 10⁹/ml
• 4.36 x 10⁹/mm³

The normal range for the RBC count varies between laboratories but is generally 4.6-6.1 10¹²/L.

Abnormalities in RBC count include:

• Erythrocytosis (> 6.1 x 10⁹/L)

Imagine that the above tubes represent spun hematocrits from 3 different patients. We will illustrate the packed RBC layer with just a few representative RBCs, whose number, size and central pallor are drawn relative to normal (Left). Middle: Note the number of RBCs can be increased (erythrocytosis) without changing the Hct or Hb. The reason that more RBCs can fit into the same packed cell volume is that the RBC size is reduced (Hct = RBC count x MCV). This is a typical picture for the individual with beta-thalassemia minor (see next slide). Right: The red cells in the right-most tube are of the same number as in the normal sample. However these cells contain little or no Hb. In this case, a normal RBC count masks a severe deficit in oxygen carrying capacity of blood.

For further discussion on erythrocytosis, click here.

Because the RBC count does not necessarily correlate with Hct or Hb (see previous 2 slides), we can usually ignore it. One exception where the RBC count may be helpful is the use of discriminant formulas for distinguishing thalassemia trait from iron deficiency.