Which laboratory result would confirm infectious mononucleosis?

Which laboratory result would confirm infectious mononucleosis?

• A. Positive Monospot test
• B. Negative Monospot test
• C. Throat culture positive for group A Streptococcus
• D. Elevated liver enzymes with normal bilirubin

Answer: (A)

A positive Monospot test confirms infectious mononucleosis because it detects heterophile antibodies that are produced during EBV infection. This rapid test directly supports the diagnosis when the clinical picture fits, making it the best confirmatory lab finding. Be aware that false negatives can occur early in the illness or in younger children, so if mono is still suspected despite a negative result, repeating the test or using EBV-specific serology can help. The other options don’t confirm mono: a throat culture positive for group A Streptococcus points to strep throat, not EBV; elevated liver enzymes with normal bilirubin can occur with mono but is non-specific and not diagnostic; a negative Monospot would argue against mono rather than confirm it.

A positive Monospot test confirms infectious mononucleosis because it detects heterophile antibodies that are produced during EBV infection. This rapid test directly supports the diagnosis when the clinical picture fits, making it the best confirmatory lab finding. Be aware that false negatives can occur early in the illness or in younger children, so if mono is still suspected despite a negative result, repeating the test or using EBV-specific serology can help. The other options don’t confirm mono: a throat culture positive for group A Streptococcus points to strep throat, not EBV; elevated liver enzymes with normal bilirubin can occur with mono but is non-specific and not diagnostic; a negative Monospot would argue against mono rather than confirm it.