Red flag findings that suggest an alternate diagnosis (even in patients known to have migraine) include the following: Pain that reaches peak intensity within a few seconds or less (thunderclap headache) Onset after age 50 Headaches that increase in intensity or frequency for weeks or longer History of cancer (brain metastases) or an immunosuppressive disorder (eg, HIV infection, AIDS) Fever, meningismus, altered mental status, or a combination Persistent focal neurologic deficits Papilledema A clear change in an established headache pattern Patients with characteristic symptoms and no red flag findings do not require testing.