Surprisingly, a monos blood test has nothing to do with mononucleosis
If your doctor says he wants you to have a monos blood test, he’s not having you tested for mononucleosis.
In fact, a monos test is part of a CBC (complete blood count) test, which analyzes the three major types of cells in blood: red blood cells, white blood cells, and platelets. It’s the most common type of test that doctors order, and is part of a routine screening that gives an indicator of overall health.
A mono test, on the other hand, is a separate test for mononucleosis. If mono is suspected, a doctor may order the mono test (also called a monospot test) and a CBC test.
The monos blood test as part of a CBC test
The CBC test counts white blood cells, measures hemoglobin (the oxygen-carrying molecule in red blood cells), estimates the red cells' volume, and sorts the white blood cells into five subtypes.
White blood cells play a critical part in the immune system, and infection or acute stress increases the number of white blood cells.
These white blood cells include monocytes, the largest of the five types, and “monos” refers to these cells. Monocytes are produced in the bone marrow and then enter the bloodstream, where they circulate in the range of 200 to 600 monocytes per microliter of blood. After a few hours they migrate to tissues such as the spleen, liver, lung, and bone marrow, where they mature into macrophages, which move to sites of infection and signal the immune system that a response is needed. They are also responsible for eliminating foreign substances.
The absolute monocytes blood test measures the percentage of monocytes in relation to all white blood cells. The normal range for the monos blood test is 2% to 8%.
Results that are out of normal range
If your test results are low, you may be at a higher risk of getting sick from an infection, particularly one caused by bacteria. A low monocytes count is medically known as monocytopenia. It can occur in response to the release of toxins into the blood by certain types of bacteria as well as in people receiving chemotherapy or corticosteroids.
If the monos blood test has a result that is lower than 2%, this can be an indication that there’s an autoimmune disorder present.
People who have had an organ transplant, for example, may have a low monos count because of the medication that’s being taken to reduce the risks of rejection.
Certain illnesses and viruses that cause inflammation with the body can also cause a low monos count. These can include malaria, tuberculosis, or an Epstein-Barr infection.
A very low count or a zero count may be an indication that there’s a serious problem with a person’s bone marrow, which is where white blood cells are manufactured. This condition is called leukopenia and it means the body can’t fight off an infection as well as it should.
A higher percentage in the monos blood test can indicate that you have some kind of infection, as the monocytes are ramped up when a bacterial infection is present.
A high count is also possible as the result of any type of illness, infection, or disease that is caused by a foreign body, such as a virus or fungal infection.
Other causes of high monos results include chronically high levels of cortisol. For this problem, a doctor would encourage you to reduce stress.
Nurse Susan, an Expert on JustAnswer, adds that several types of cancer can also cause an increase in monocytes, as can chronic ulcerative collitis, collagen disease, and some parasitic disorders.
A high monos count may also be an indication of an untreated autoimmune disorder, such as rheumatoid arthritis. In addition, high monos levels can indicate:
- Chronic inflammatory disease
- Chronic ulcerative colitis
- Collagen disease
The indicator for mononucleosis is the reason why the CBC, including the monos test, is often ordered along with the monospot test.
It’s also important to note that some people have a naturally high count of monocytes, which will be indicated over time with repeated monos blood tests.
Other issues with the monos test
Other questions about the monos test often arise at JustAnswer. One customer who had had blood work done was concerned about a monocyte result that read “4.2 L.” Dr. Steve explained that “auto” meant the monocyte percentage was estimated by an automated cell counter.
The “L” indicated that the number was on the low side, but, as Dr. Steve said, “It’s still considered in acceptable range.”
Dr. Charles, another Expert on JustAnswer, reassured another customer that the normal values of monocytes in a test result can vary widely from lab to lab. Even a 1% result, without other symptoms of concern, means “there’s nothing of concern and it is normal values.”
For a customer with a monocyte result of 10.3, Dr. Arun, also an Expert on JustAnswer, was equally reassuring. “A life threatening condition is unlikely,” he wrote to the nervous customer. In fact, a probable explanation lay in an autoimmune disorder that had been diagnosed previously.
In short, small variations outside the acceptable levels are rarely indicative of any serious, previously undiagnosed problems. The CBC test and the monos blood test are good general indicators of health, but there are many more specific tests that are required to diagnose serious illness.
The most important thing to remember when researching your CBC results is to avoid consulting Dr. Internet! Be sure to consult your own doctor, or when you need a fast, reliable answer, to consult the medical Experts on JustAnswer.com.
Have you ever had an elevated or low monos level diagnosed? Please share your experience with us in the comments below.
This post was first published in 2017 and is regularly updated.