Will I have to take an enema before a rectal exam?

No. Rectal exam as part of a physical exam, i.e. Insertion of a gloved, lubricated finger into the rectum, does not need an enema. Anoscopy (insertion of a short tube into the anus to view the area generally does not unless surgical work is planned. Examination with a sigmoidoscope (rigid or flexible) does need enemas.