A good example is an egg allergy, which may not seem important when having surgery; however, many medications are formulated in an egg base, which could cause a serious reaction if given to the patient.
If a patient begins to feel ill or has a fever in the days preceding surgery, the surgeon needs to be made aware. The surgeon may decide it is safe to continue with surgery or may opt to postpone the procedure. A fever is a sign of possible infection and should be disclosed, to prevent wasted time and energy for both the patient and the surgeon.
A patient who presents at the hospital for a scheduled surgery unaware that they have a fever may be sent home and the surgery appointment changed.