Monospot Test

A monospot test is used to diagnose infectious mononucleosis (often referred to as mono). It detects certain antibodies that the body produces to fight the viruses that cause the disease. Since it takes awhile for antibodies to develop, the first test can be inaccurate and may need to be repeated one to two weeks after the symptoms first appear.

What Is the Monospot Test?

A monospot test is a blood test that is used to help diagnose mononucleosis, also known as "mono."
 

How Does a Monospot Test Work?

A monospot test works by detecting certain proteins called heterophile antibodies. The body makes these proteins to fight the Epstein-Barr virus (EBV) or cytomegalovirus (CMV) -- the two viruses that cause mono (see Mononucleosis Causes).
 

Can a Person With Mono Have a Negative Test?

Since it takes time for antibodies to develop after you're infected, it's possible for the first monospot test to be negative, even if you have the disease. The doctor may need to order or repeat the test one to two weeks after you develop possible symptoms of mono.
 
At that time, the monospot test comes back positive (meaning that a mono infection is present) in about 85 percent of people with the disease.
 

Can a Person Without Mono Have a Positive Test?

It's possible for a person to have a positive monospot test and not have mononucleosis. A positive result can also occur in people with:
 
  • Lymphoma
  • Systemic lupus erythematosus (lupus)
  • Certain gastrointestinal cancers.
     

Other Tests to Diagnosis Mono

If the doctor suspects mono based on your symptoms and physical exam, he or she can order other tests besides the monospot test. Additional tests that can help your doctor make a mononucleosis diagnosis include:
 
  • A complete blood count (CBC) to see if your blood platelet count is lower than normal and if your lymphocytes (lymph cells) are abnormal
  • A chemistry panel to see if your liver enzymes are abnormal.
 
Also, if your throat is sore, having a throat culture is usually a good idea for several reasons. First, the symptoms of mono and strep infection -- including that caused by strep-A (a particularly serious form of strep bacteria) -- are similar. Second, strep throat or other throat infections can develop at any time during or shortly after mononucleosis.
 
In any case, it's important that throat infections be diagnosed as soon as possible and treated with antibiotics that can kill the organism responsible for the infection.
 
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Information on Mono

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