Initial Investigations for Delirium
All patients with suspected delirium should undergo a focused laboratory workup including complete blood count, comprehensive metabolic panel, urinalysis, blood glucose, and thyroid function tests, with neuroimaging reserved for those with focal neurological deficits, head trauma, new seizures, or unexplained altered mental status. 1
Essential First-Line Laboratory Tests
The initial workup should be guided by clinical evaluation rather than performed as an extensive routine battery 1. The following tests are recommended for nearly all patients:
- Complete blood count (CBC) to evaluate for infection or hematologic abnormalities 1, 2
- Comprehensive metabolic panel to assess electrolyte imbalances, renal and liver function 1, 2
- Urinalysis and urine culture to screen for urinary tract infections, a common precipitating factor 3, 1
- Blood glucose measurement to rule out hypo/hyperglycemia 1, 2
- Thyroid function tests (TSH) to evaluate for thyroid disorders 3, 1
Additional Laboratory Tests Based on Clinical Context
Consider these tests when specific etiologies are suspected:
- Medication levels when appropriate, especially for patients on psychotropic medications 2
- Toxicology screen to assess for substance intoxication or withdrawal 2
- Vitamin B12, folate, and methylmalonic acid (MMA) if nutritional deficiency is suspected 3
- Ammonia level in patients with liver disease 3
- Arterial blood gas if hypoxia or hypercarbia is suspected 1
Neuroimaging: Selective, Not Routine
Neuroimaging should be selective rather than routine, guided by specific clinical features 1. Brain CT or MRI is indicated when:
- Focal neurological deficits are present 1, 2
- History of recent head trauma exists 1, 2
- New-onset seizures occur 1, 2
- Signs of increased intracranial pressure are evident 1, 2
- Unexplained altered mental status persists despite initial workup 1, 2
MRI may be preferred when available, though practical challenges exist with agitated patients who cannot follow commands 2.
Additional Diagnostic Studies
- Electrocardiogram (ECG) to assess for myocardial ischemia or arrhythmias 1, 2
- Chest radiography to evaluate for pneumonia or other pulmonary processes 3, 1
- Electroencephalography (EEG) when seizure activity is suspected 2
- Lumbar puncture to assess for central nervous system infection when clinically indicated (consider if fever, meningismus, or immunocompromised state) 2
Delirium Screening Tools
Use the Confusion Assessment Method (CAM) or CAM-ICU to objectively diagnose delirium 1, 4. These validated tools assess:
- Acute onset and fluctuating course
- Inattention
- Disorganized thinking
- Altered level of consciousness
The CAM-ICU is specifically designed for ICU patients with very good psychometric properties 1, while the 3-minute diagnostic CAM (3D-CAM) is efficient for general hospital settings 4.
Critical Pitfalls to Avoid
- Failing to recognize hypoactive delirium, which is the most commonly missed subtype 1, 5
- Attributing symptoms to dementia without investigating for acute causes—delirium superimposed on dementia is frequently overlooked and carries worse outcomes including higher 30-day readmission rates 1, 6
- Inadequate screening in emergency settings leading to missed diagnosis 1, 5
- Performing extensive neuroimaging without clinical indication, which wastes resources and delays treatment 1
Common Underlying Causes to Investigate
Focus your clinical assessment on these frequent precipitants 1:
- Infections (urinary tract, pneumonia, sepsis)
- Medications (anticholinergics, benzodiazepines, opioids)
- Metabolic disturbances (electrolyte abnormalities, hypoglycemia, uremia)
- Substance intoxication or withdrawal (alcohol, sedatives)
- Neurological conditions (stroke, seizures, intracranial hemorrhage)