Pharmacotherapy Newsletter

Volume 1, Issue 20, 06/01/2009

Question

What is the mechanism by which glucocorticoids (e.g., dexamethasone, methylprednisolone, prednisone) increase the white blood cell (WBC) count?

Answer

Part 1 of a 2 part series.  The white blood cell (WBC) count is a routine laboratory test that reflects the number of leukocytes (or WBC) distributed in the blood.  The leukocytes that make up a typical WBC count on a lab analysis include neutrophils at 60-70%, lymphocytes at 28%, monocytes at 5%, eosinophils at 2-4%, and basophils at 0.5%.¹  When a WBC count is performed, the values reflect the leukocytes distributed within the blood and not those in the bone marrow, tissue or attached to the endovascular lining of blood vessels.  It is evident that the neutrophils make up the greatest percentage of leukocytes and thus can have the greatest impact on changes in the WBC count.  Neutrophils are also called polymorphonuclear leukocytes (PMN) because of the number of stages they go through during their life cycle.  They are initially released from the bone marrow as immature neutrophils that are characterized as having a nonsegmented, band like appearing nucleus.  As such, these immature neutrophils are called "bands".  An increase in the number of these immature neutrophils in circulation can be indicative of a bacterial infection for which they are being generated to fight.  This is known as the "left shift" seen in a WBC differential.²  As the immature neutrophils become activated or exposed to bacterial pathogens, their nucleus will take on a segmented appearance due to increases gene transcription.  These and other neutrophils can be found in several compartments in the body, but the two compartments that relate most to this newsletter are the marginal compartment (those neutrophils attached to the endothelium of the blood vessel) and the circulating compartment (those circulating in the blood vessels along with other cells).  Understanding this information is critical for the proper assessment of an elevated WBC count, especially when glucocorticoids (e.g., dexamethasone, methylprednisolone, prednisone) have been administered to the patient.