The Test Sample
What is being tested?
Epstein-Barr virus causes an infection that is very common. According to the Centers for Disease Control and Prevention (CDC), as many as 95% of people in the United States will have been infected by EBV by the time they are 40 years old. The virus is easily passed from person to person. It is present in the saliva of infected individuals and can be spread through close contact such as kissing and through sharing utensils or cups.
After initial exposure to EBV, there is a period of several weeks before associated symptoms may appear called the incubation period. During the acute primary infection, the virus multiplies in number. This is followed by a decrease in viral numbers and resolution of symptoms, but the virus never completely goes away. Latent EBV remains in the person's body for the rest of his life and may reactivate but usually causes few problems unless the person's immune system is significantly weakened.
Most people are infected by EBV in childhood and experience few or no symptoms. However, when the initial infection occurs in adolescence, it can cause infectious mononucleosis, commonly called mono, a condition associated with fatigue, fever, sore throat, swollen lymph nodes, an enlarged spleen, and sometimes an enlarged liver. These symptoms occur in about 35% to 50% of infected teens and young adults and usually resolve within a month or two.
People with mono are typically diagnosed by their symptoms and the findings from a complete blood count (CBC) and a mono test (which tests for a heterophile antibody). About 10% to 20% of those with mono will not produce heterophile antibodies and will have a negative mono test; this is especially true with children. Tests for EBV antibodies can be used to determine whether or not the symptoms these people are experiencing are due to a current infection with the EBV virus.
Sometimes, it can be important to distinguish EBV from other illnesses. For instance, it may be important to diagnose the cause of symptoms of a viral illness in a pregnant woman. Testing can help to distinguish a primary EBV infection, which has not been shown to affect a developing baby, from a cytomegalovirus (CMV), herpes simplex virus, or toxoplasmosis infection, as these illnesses can cause complications during the pregnancy and may harm the fetus. It can also be important to rule out EBV infection and to look for other causes of the symptoms. Those with strep throat, an infection causes by Group A streptococcus, for instance, need to be identified and treated with antibiotics. A person may have strep throat instead of mono or they may have both conditions at the same time.
Several tests for different types and classes of EBV antibodies are available. The antibodies are proteins produced by the body in an immune response to several different Epstein-Barr virus antigens. During a primary EBV infection, the level of each of these EBV antibodies rises and falls at various times as the infection progresses. Measurement of these antibodies in the blood can aid in diagnosis and typically provides the doctor with information about the stage of infection and whether it is a current, recent, or past infection.
|Antibody||Timing of when the antibody is typically detected in the blood|
|Viral Capsid Antigen (VCA)-IgM antibody||Appears first after exposure to the virus and then tends to disappear after about 4 to 6 weeks|
|VCA-IgG antibody||Emerges during acute infection with the highest level at 2 to 4 weeks, then drops slightly, stabilizes, and is present for life|
|Early Antigen (EA-D) antibody||Appears during the acute infection phase and then tends to disappear; about 20% of those infected will continue to have detectable quantities for several years after the EBV infection has resolved.|
|Epstein-Barr Nuclear Antigen (EBNA) antibody||Does not usually appear until the acute infection has resolved; it develops about 2 to 4 months after the initial infection and is then is present for life.|
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.