What is the difference between a symptom and a sign?

Medical Author: William C. Shiel Jr., MD, FACP, FACR

A symptom is any subjective evidence of disease, while a sign is any objective evidence of disease. Therefore, a symptom is a phenomenon that is experienced by the individual affected by the disease, while a sign is a phenomenon that can be detected by someone other than the individual affected by the disease. For examples, anxiety, pain, and fatigue are all symptoms. In contrast, a bloody nose is a sign of injured blood vessels in the nose that can be detected by a doctor, a nurse, or another observer.

Health care professionals use symptoms and signs as clues that can help to determine the most likely diagnosis when illness is present. Symptoms and signs are also used to compose a listing of the possible diagnoses. This listing is referred to as the differential diagnosis. The differential diagnosis is the basis from which initial tests are ordered to narrow the possible diagnostic options and choose initial treatments.