Mononucleosis (also called “mono”) is an illness caused by the Epstein-Barr virus (EBV). A different virus, cytomegalovirus (CMV), can cause symptoms similar to mono, but CMV is less common.

Mono is most common in young adults between the ages of 15 and 25. The virus is spread by kissing, sharing a drinking glass or eating utensils, and through sexual contact with an infected person.

The tests for mono detect antibodies against EBV in a sample of blood. The antibodies are substances (proteins) produced by the immune system to fight the infection.

Once they are formed, antibodies usually persist for the rest of a person's life.

• Monospot test (heterophil test). This quick screening test detects a mono infection that is just developing. A sample of blood is placed on a microscope slide and mixed with other substances. If mono is present, the blood clumps (agglutinates). This usually indicates the presence of antibodies (called heterophil antibodies) against EBV. Monospot testing can usually detect antibodies against EBV 2 to 9 weeks after a person is infected. It is generally not used to diagnose mono that started more than six months earlier.
• EBV antibody test. For this test, a sample of blood is mixed with a substance that attaches to antibodies against EBV. A series of tests can detect different types of antibodies to help determine whether a person was infected recently or sometime in the past.

This test is done on a blood sample taken from a vein.

Mononucleosis Tests
Results

The results of the antibody test to detect Epstein-Barr virus (EBV) are usually given in titers. A titer is a measure of how much the blood sample can be diluted before the antibodies against the Epstein-Barr virus (EBV) can no longer be detected.

A titer of 1 to 10 (1:10) means that antibodies can be detected when 1 part of the blood sample is diluted by up to 10 parts of a salt solution (saline). A larger second number means there are more antibodies in the blood. Therefore, a titer of 1 to 80 indicates more EBV antibodies in the blood than a titer of 1 to 10.

The EBV antibody test can also detect the type of antibodies present in the blood. This indicates whether the infection is recent or old.

EBV antibody test
Normal:	The titer is less than 1 to 10 (1:10).
Abnormal:	A titer greater than 1 to 10 (1:10) usually indicates mononucleosis. However, other diseases that can cause a positive result include some types of cancer (such as leukemia or Burkitt's lymphoma), hepatitis, and rheumatoid arthritis.