Is infectious mononucleosis contagious before symptoms appear? how long do you have to wait to get tested after symptoms appear?

Likely, immediately : Mono is a common infection triggered in most cases by the EB virus. About 90% of adults will show past infections, many from childhood illness that is often mild. Since the disease can vary in intensity from no symptoms at all to death, the contagious period is hard to pin down. The incubation period is 30-50 days. Some office tests may not pick it up when symptoms appear but IgM would be positive