Patients with signs or symptoms of a medical disorder should have testing appropriate to diagnose that disorder: Head CT: Patients with new-onset mental symptoms or with delirium, headache, history of recent trauma, or focal neurologic findings (eg, weakness of an extremity) Lumbar puncture: Patients with meningeal signs or with normal head CT findings plus fever, headache, or delirium Thyroid function tests: Patients taking lithium, those with symptoms or signs of thyroid disease, and those > 40 years with new-onset mental symptoms (particularly females or patients with a family history of thyroid disease) Chest x-ray: Patients with low oxygen saturation, fever, productive cough, or hemoptysis Blood cultures: Seriously ill patients with fever Liver tests: Patients with symptoms or signs of liver disease, with a history of alcohol or drug use disorder, or with no obtainable history Less often, findings may suggest testing for systemic lupus erythematosus, syphilis, demyelinating disorders, Lyme disease, or vitamin B12 or thiamin deficiency, especially in patients presenting with signs of dementia.