Infectious mononucleosis (IM), caused by the Epstein-Barr virus (EBV), is an extremely common disease process in the United States and around the world.  Nearly 90 to 95 percent of the world’s adult population has evidence of EBV infection through seroconversion. Though often subclinical in the young pediatric population, clinical symptomatology is very common in adolescent and young adult aged patients.  Commonly, symptomatic patients present with malaise, fatigue, fever, pharyngitis, tonsillitis, and lymphadenopathy.  Diagnostically, this creates a dilemma due to the potential for many other causes for these symptoms.   Several laboratory tests have been developed to aid in the diagnosis of IM.  Currently, serum testing for EBV-specific antibodies is considered the gold standard for diagnosis, but rapid results are usually not obtainable.  Because of this time delay, several other testing modules have been created with the most widely used test being the mononuclear spot test or, monospot test. The basis of the monospot test is blood agglutination, much like the Paul-Bunnell test which was developed prior to the monospot test.  The monospot test is a latex agglutination test which utilizes equine erythrocytes as the primary substrate and tests for specific heterophile antibodies produced by the human immune system in response to EBV infection. When these specific antibodies are present in the patient's blood specimen, exposure to equine erythrocytes will lead to clumping of the sample, thus signaling a positive agglutination reaction. This reaction is considered a positive test and therefore a diagnostic confirmation of the clinically suspected IM.  Though the monospot test is considered to be a very specific test, the sensitivity falls in the range of 70 to 90% and is particularly weak among children under the age of four years old. Because of this low sensitivity, the Center for Disease Control does not recommend the monospot test for the diagnosis of clinical infectious mononucleosis.