Which diagnostic test is used for suspected infectious mono?

• A. Heterophile test
• B. Throat culture
• C. Blood culture
• D. Lymph node biopsy

Answer: (A)

When evaluating suspected infectious mononucleosis, the first step is to look for heterophile antibodies produced during EBV infection. The heterophile antibody test (often called a Monospot) is a rapid, inexpensive screen that detects these antibodies by their ability to agglutinate animal red blood cells. A positive result supports the diagnosis, especially in adolescents and young adults who present with fever, sore throat, swollen glands, and fatigue. The test is most reliable several days after symptoms begin when antibody levels are higher; a negative result early in illness or in young children does not completely rule out mono, so EBV-specific serology (like VCA IgM and IgG, EBNA) or EBV DNA testing may be pursued if suspicion remains high.

Other options don’t fit as initial tests for mono. A throat culture targets bacteria such as group A Streptococcus and won’t diagnose EBV infection. Blood cultures are used to detect bacteremia, not viral mononucleosis. Lymph node biopsy is an invasive procedure reserved for persistent, concerning lymphadenopathy where malignancy or other pathology is suspected, not for routine mono evaluation.

So, the heterophile antibody test is the best initial diagnostic tool for suspected infectious mononucleosis.