In the majority of cases, delirium is caused by an illness outside the central nervous system. Assessment includes thorough history taking and physical examination. Laboratory tests including complete blood cell count, urinalysis, and blood chemistry profile are indicated. In most cases a chest radiograph should be obtained to rule out pneumonia or other pulmonary processes. Thyroid profile, electrocardiogram, toxic drug screening, vitamin B12 levels, and magnesium concentrations may also be useful.
Brain imaging is necessary if structural disease of the central nervous system is suspected.
An electroencephalogram usually reveals generalized slowing of brain-wave patterns in delirium, and therefore its use may in some cases clarify the diagnosis. Arterial blood gas measurements are useful if the physician suspects hypoxia, hypercarbia, or other acid-base derangements. HIV testing is indicated if risk factors are present. More invasive or elaborate studies such as lumbar puncture are done only if specifically indicated. A psychiatric history should always be obtained and a mental status examination performed.