Reading a CBC, Monocytes

Monocytes may be counted by machines or by a technician doing a manual differential or "manual diff".  This involves taking a drop of blood and making a smear on a slide.  It is allowed to dry, then stained with Diff Quick stain.  Once the stain has dried the slide is viewed under a microscope and evaluated for red and white blood cell morphology as well as a count of 100 white blood cells to determine what percent of cells are of each WBC type including monocytes.

The number of monocytes may be expressed as a percent or as an absolute number which is expressed as some number per microliter.  If you have a choice it is best to work with the absolute number since, with abnormal WBC counts, the number expressed as a percent can be misleading.

Below is a photo of a normal monocyte:

Monocytes are the cleanup crew for the body.  They migrate out of the blood vessels as needed and then become tissue macrophages, which means they eat dead tissue and anything else that doesn't belong in the body.

Increased monocytes or "monocytosis" is caused by:
 -Inflammation: either acute or chronic
-Stress: due to natural or administered steroids, especially in dogs.

Decreased monocytes or "monocytopenia" is caused by:
-Pancytopenia: usually an incidental finding when all white blood cell counts are low which is called "pancytopenia".