Laboratory tests that may be helpful for diagnosis include the following:
Complete blood cell count with differential - Helpful to diagnose infection and anemia
Electrolytes - To diagnose low or high levels
Glucose - To diagnose hypoglycemia, diabetic ketoacidosis, and hyperosmolar nonketotic states
Renal and liver function tests - To diagnose liver and renal failure
Thyroid function studies - To diagnose hypothyroidism
Urine analysis - Used to diagnose urinary tract infection
Urine and blood drug screen - Used to diagnose toxicological causes
Thiamine and vitamin B-12 levels - Used to detect deficiency states of these vitamins
Tests for bacteriological and viral etiologies including syphilis
Drug screen including alcohol level
Tests for other infectious causes if necessary or clinically indicated (These tests are not performed routinely, even though 30-40% of hospitalized patients with HIV infection develop delirium during hospitalization.  )
Serum marker for delirium: The calcium-binding protein S-100 B could be a serum marker of delirium. Higher levels are seen in patients with delirium when compared to patients without delirium. 
See the list below:
- Perform CT scan of the head.
- Magnetic resonance imaging (MRI) of the head may be helpful in the diagnosis of stroke, hemorrhage, and structural lesions.
- In delirium, generally, slowing of the posterior dominant rhythm and increased generalized slow-wave activity are observed on electroencephalogram (EEG) recordings.
- In delirium resulting from alcohol/sedative withdrawal, increased EEG fast-wave activity occurs.
- In patients with hepatic encephalopathy, diffuse EEG slowing occurs.
- The type of patterns observed includes triphasic waves in toxicity or metabolic derangement, continuous discharges in nonconvulsive status epilepticus, and localized delta activity in focal lesions.
Chest radiograph is used to diagnose pneumonia or congestive heart failure.
Lumbar puncture is indicated when CNS infection is suspected as a cause of delirium or when the source for the systemic infection cannot be determined.
Pulse oximetry is used to diagnose hypoxia as a cause of delirium.
Electrocardiogram is used to diagnose ischemic and arrhythmic causes.
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