Mononucleosis (EBV) Testing

Section Editor: Rodney E. Rohde PhD
June 3, 2026

Infectious mononucleosis, usually called mono, is an illness most often caused by the Epstein-Barr virus (EBV). EBV is a very common virus, and most people are infected by it at some point in life, often without ever knowing. When it does cause illness, mono is most common in teenagers and young adults, with symptoms such as extreme tiredness, sore throat, fever, and swollen glands. Testing for mono usually involves a quick screening test and, in some cases, more specific EBV antibody tests.

This article explains the tests used to diagnose mono, what the wording on your report means, and how the EBV antibody results show whether an infection is recent or in the past, so you can better understand a report you have received.

What is mononucleosis, and what causes it?

Mono is most often caused by EBV, which spreads through saliva, one reason it is sometimes called the “kissing disease.” After an EBV infection, the virus stays in the body for life, and in many people, especially young children, it causes no symptoms at all. A few other infections, including one caused by a virus called cytomegalovirus (CMV), can cause a very similar illness, so testing helps confirm whether EBV is the cause.

The monospot (heterophile antibody) test

The quick screening test for mono is the Monospot test, which detects heterophile antibodies. Antibodies are proteins that the immune system makes in response to an infection, and heterophile antibodies are a particular group that the body produces during an EBV mono infection, even though they are not specifically directed against EBV. The result is reported as positive or negative.

The monospot is fast and useful, but it has limits that are worth knowing:

It can be negative early — Heterophile antibodies take time to appear, so a monospot done in the first week of illness can be negative even when a person has mono. It may be repeated, or EBV-specific tests may be done.
It is less reliable in young children — who often do not make these antibodies, even when they have an EBV infection.
It does not detect EBV directly — so when a clearer answer is needed, the more specific EBV antibody tests below are used.

EBV-specific antibody tests

When more detail is needed, the laboratory tests for antibodies specific to EBV. The three most common are described below. Their timing is what makes them useful, as they appear and disappear at different points during an infection. (IgM and IgG antibodies are explained in a separate article.)

Viral capsid antigen IgM (VCA IgM) — Appears early and fades within weeks to a few months. A positive result points to a recent or current infection.
Viral capsid antigen IgG (VCA IgG) — Appears early and then stays positive for life. A positive result means you have been infected with EBV, either now or in the past.
Epstein-Barr nuclear antigen IgG (EBNA IgG) — Appears later, usually several weeks to months after the infection begins, and then stays positive for life. Because it shows up late, a positive EBNA result generally means the infection is not brand new.

How to read your EBV results together

Reading EBV antibody levels as a group shows where you are in an infection. The combinations below cover the most common patterns.

Recent (current) EBV infection — VCA IgM positive and VCA IgG positive, with EBNA negative. The early antibodies are present, but the late ones have not yet appeared, suggesting a new infection.
Past EBV infection — VCA IgM negative, VCA IgG positive, and EBNA positive. You were infected at some time in the past and have recovered. This pattern means EBV is unlikely to be the cause of a current illness.
No previous EBV infection — VCA IgM, VCA IgG, and EBNA all negative. You have not been infected with EBV. If you have symptoms, it may be too early in an infection for antibodies to show, or the illness may have another cause.

What your blood count might show

Mono often produces changes on a complete blood count (CBC), a common blood test that counts the different types of blood cells. Your report may mention a high number of lymphocytes (a type of white blood cell) and may describe some of them as atypical or reactive lymphocytes. This wording sounds alarming, but it simply means the cells have changed their appearance as they respond to the virus. In the setting of mono, this is an expected finding and is not a sign of a blood cancer such as leukemia.

What happens after these tests

Mono is usually diagnosed from a combination of your symptoms and your test results, and those results inform the decisions you and your healthcare team make together rather than dictating them on their own.

There is no specific antiviral medicine that cures mono. Care focuses on rest, fluids, and easing symptoms while the body clears the infection on its own. Most people recover fully, although tiredness can last for several weeks. Because the spleen, an organ in the upper left part of the abdomen, can become enlarged during mono, doctors often advise avoiding contact sports and heavy lifting for a period of time to lower the small risk of injuring it; follow your own doctor’s advice about when it is safe to return to your usual activities. After the infection, EBV stays in the body in an inactive form for life, as other viruses in its family do, and usually causes no further trouble. In certain situations, such as in people with a weakened immune system, a different test that measures the amount of EBV directly (an EBV viral load, or PCR test) may be used, but this is not part of the usual testing for mono.

Questions to ask your doctor

Based on my tests, do I have a recent EBV infection, a past one, or no infection at all?
If my monospot was negative but I have symptoms, could it be too early, and should I have EBV-specific tests?
What did my blood count show, and do the “atypical lymphocytes” mean anything serious?
Could my illness be caused by something other than EBV?
How long should I expect the tiredness and other symptoms to last?
Is my spleen affected, and when is it safe to return to sports or heavy activity?
Is there anything I can do to feel better or recover more quickly?
Can I pass this on to others, and for how long?
Will EBV cause me any problems in the future?
Who should I contact if my symptoms get worse?