How Soon Do Tests Show If You Have Mono?

How soon after the symptoms begin will a blood test show if you have mono?

It all depends on the test.

When checking for mono, doctors may do one of several different types of blood tests. If someone has symptoms of mono, the doctor often does a blood test called a "monospot." If the monospot is positive, it's pretty accurate, meaning that the person likely has mono. But it can sometimes take a couple of weeks for the monospot to detect the infection. So when symptoms first start, a monospot test may be negative, even though the person really has mono.

If a doctor still thinks you have mono after the monospot comes back negative, he or she may want to do some different blood tests. These can show the infection as soon as symptoms appear. Other tests can show if a person had mono in the past.

Reviewed by: Larissa Hirsch, MD
Date reviewed: February 2009

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