Acute appendicitis, usually, is an emergency case, so, very often people suspected of having appendicitis may be taken to surgery before the diagnosis is certain.
Surgery is diagnostic and therapeutic at the same time.

History of symptoms about abdominal pain, nausea and vomiting with fever, and physical examination of abdomen that reveals abdominal tenderness, are enough to suspect possible appendicitis.
Blood testing for elevated white blood cells, abdominal x-ray, abdominal ultrasound, an x-ray test with a liquid barium and CT scan, are all diagnostic procedures helpful in making a diagnosis of appendicitis.