A small number of people with mononucleosis may never have a positive test. The highest number of antibodies occurs 2 to 5 weeks after mono begins. They may be present for up to 1 year. In rare cases, the test is positive even though you do not have mono.

Will my mono test always be positive?

Monospot-like tests may not turn positive for up to 4 weeks. Moreover, children younger than 8 years are less likely to ever produce heterophile antibody, so the test isn't useful in that age group. In addition, a positive monospot isn't always caused by currently active mononucleosis.

Does mono stay in your blood forever?

If you get mono, the virus stays in your body for life. That doesn't mean that you're always contagious . But the virus can surface from time to time and risk infecting someone else.