Is the ampicillin rash the new MonoSpot for EBV?

the sensitivity of the monospot for EBV is 85%. if you give ampicillin to a patient with EBV, >90% will get a maculopapular rash. this means that if a person has infectious mono, they are more likely to break out into a rash after receiving ampicillin than having a positive monospot test.

fyi: up to 80% of patients with CLL also break out into a rash after receiving ampicillin.