Blumberg's sign, also referred to as rebound tenderness, is a clinical sign that is elicited during physical examination of a patient's abdomen by a doctor or other health care provider. It is indicative of peritonitis. It refers to pain upon removal of pressure rather than application of pressure to the abdomen. (The latter is referred to simply as abdominal tenderness.)
The abdominal wall is compressed slowly and then rapidly released. A positive sign is indicated by presence of pain upon removal of pressure on the abdominal wall. It is very similar to rebound tenderness and might be regarded by some authors as the same thing, or at least a particular application of it.
However, in recent years the value of rebound tenderness has been questioned, since it may not add any diagnostic value beyond the observation that the patient has severe tenderness. Use of the sign has been supported by others.