A mono blood test is a test that looks for signs in your blood that you have the Epstein-Barr virus (EBV), which is a common virus that causes infectious mononucleosis, or mono. Mono is passed from person to person through saliva, and symptoms usually appear within 4 to 6 weeks after exposure and ease in 1 to 2 months. If you have mono, you may have a high level of a type of white blood cell called a lymphocyte in your blood. Your immune system also will make certain types of antibodies (heterophile antibodies) to fight off the EBV. These antibodies will also appear in your blood if you have mono.

It is important to note that a mono blood test is different from a test that measures monocytes, which are a type of white blood cell that help fight infections. A complete blood count (CBC) is a routine blood test that measures the levels of different types of blood cells, including monocytes, in your blood. A normal monocyte count is between 2% and 8% of your white blood cell count, which equals about 100 to 700 monocytes per microliter of blood in healthy adults. If your monocyte count is outside those ranges, you may be at risk of acquiring a monocyte-related condition.

In summary, a mono blood test is a test that looks for signs of the Epstein-Barr virus in your blood, while a test that measures monocytes is a routine blood test that measures the levels of different types of blood cells, including monocytes, in your blood.