Have you had glandular fever? This is how antibodies reveal your immunity

It is common to be unsure whether you have had glandular fever. In adults, the infection usually causes clear and pronounced symptoms that are difficult to miss, while children usually have very mild or nonspecific symptoms. Since Epstein-Barr virus (EBV) remains in the body after infection, an antibody test can tell you whether you have already had the virus and are therefore immune. The test is not used to investigate prolonged fatigue, but is primarily a check of your immunity status.

How do you know if you have had glandular fever? This is how IgG and IgM antibodies show whether you have or have had EBV

Glandular fever, or infectious mononucleosis, is most often caused by EBV. The virus belongs to the herpes virus family and remains in the body after infection, but this does not mean that you are sick all the time. What makes blood tests useful is that the immune system forms different antibodies at different times during the infection.

When talking about EBV tests, they usually mean a combination of antibodies against different parts of the virus. The most important for interpretation are IgM, IgG against VCA and IgG against EBNA. It is the combination of these markers that helps the doctor or laboratory assess whether the infection is current, recent or old.

What symptoms does glandular fever usually cause?

Glandular fever often causes a sore throat, fever, severe fatigue and swollen lymph nodes, especially in the neck. Some people also get tonsils, headaches, body aches or a feeling that recovery takes much longer than with a common cold. Liver damage and an enlarged spleen can also occur.

In teenagers and young adults, the infection is often more noticeable. In young children, however, EBV can cause mild or nonspecific symptoms, which means that many people do not know when they were infected. Therefore, it is common for adults to later discover through blood tests that they have already had EBV earlier in life.

A typical example is the person who was bedridden for two weeks during high school with flu-like symptoms, but was never tested. Another example is someone who wants to find out their immunity for a future treatment, pregnancy or simply wants to confirm whether they are protected against the virus. In such situations, EBV serology can provide a more accurate answer than the memory of the symptoms.

How do IgG and IgM antibodies show whether you have or have had EBV?

To understand an EBV test, you need to know what the antibodies mean over time. IgM is usually an early response from the immune system, while IgG often comes a little later and can persist for a long time, sometimes for life. For EBV, however, it is not enough to just look at “IgG positive” or “IgM positive” in isolation.

In primary, i.e. first, EBV infection, VCA IgM is often seen as positive and VCA IgG is positive, while EBNA IgG has not yet had time to become positive. The CDC describes that people with anti-VCA IgM but without antibodies to EBNA are typically considered to have a primary infection. VCA IgM usually appears early and usually disappears within four to six weeks.

VCA IgG also appears early, peaks within about two to four weeks after the onset of symptoms and then usually remains for life. If you have VCA IgG and EBNA IgG but not VCA IgM, this usually indicates that you have had the infection before, not that you have a new glandular fever right now. This is the most common picture in adults.

EBNA IgG is particularly valuable for distinguishing between recent and old infection. This antibody is not normally seen in the acute phase but only develops after two to four months and then remains for a very long time. Therefore, in practice, a positive EBNA IgG often means that the infection is not completely recent.

There are also patterns that are more difficult to interpret. Sometimes several antibodies are positive at the same time, or the test result does not fit perfectly into the standard patterns. In this case, the laboratory may need to weigh symptoms, time since illness and sometimes additional tests to provide a fair interpretation.

What does a positive IgG mean if you are wondering if you have had glandular fever?

If your test shows positive EBV IgG, especially together with positive EBNA IgG, it usually means that you have had EBV before. However, it does not say exactly when you were sick. The infection may have occurred a few months ago, during your teens or even earlier.

This is a common question among people seeking treatment for chronic fatigue: “Can my positive IgG explain how I feel now?” The answer is that a positive IgG primarily indicates a previous infection, not automatically that today's symptoms are caused by EBV. Since the antibodies often persist for life, the test result must always be interpreted together with symptoms and other findings.

If VCA IgG is positive but EBNA IgG is negative, the picture can sometimes indicate an early infection, but it can also require caution in interpretation depending on the analysis method and the patient's situation. This is especially true if the person is immunocompromised or if the sample was taken very early in the course of the disease. In that case, further assessment may be needed.

When is EBV testing particularly relevant?

EBV testing is most helpful when the symptoms are similar to glandular fever but the picture is not entirely typical, or when you want to understand whether a previously suspected episode was really EBV. Specific antibody tests may be valuable in people who do not have a typical mononucleosis picture or when other EBV-related conditions need to be assessed.

Testing may also be relevant if you have had:

• prolonged fatigue after fever and sore throat
• recurring questions about previous glandular fever
• need for medical clarity before exercise, work or further investigation
• test results where a rapid test for mononucleosis was negative but the suspicion still remains

The classic Monospot test is still used in some places, but is not recommended for general use because it can give both false positive and false negative results. The test is less reliable, especially in children. More specific EBV serology with VCA IgM, VCA IgG and EBNA IgG therefore often provides better guidance.

When should you seek medical attention or refrain from exercise?

If acute glandular fever is suspected, you should be careful with strenuous physical activity, especially contact sports. One reason is that the spleen may be enlarged during the illness phase, which increases the risk of injury. It is recommended that you avoid contact sports until you have fully recovered.

You should seek medical attention if you have severe throat pain, severe difficulty swallowing, respiratory problems, persistent high fever, severe pain under the left rib cage, or if your fatigue is so severe that it interferes with your daily life. This also applies if the symptoms do not fit with a common viral infection or if you have other diseases that affect the immune system. EBV-like symptoms can in some cases be due to other infections and then need to be investigated in another way.

A blood test cannot replace a comprehensive medical assessment, but it can provide something that many people ask for: clarity. For some, it means that you can let go of an old suspicion. For others, the test result becomes the starting point for further searching for other causes of fatigue, throat problems, or recurring malaise.