Laboratory Evaluation for New Onset Psychosis
For patients with new onset psychosis, a comprehensive laboratory workup should include complete blood count, basic metabolic panel, liver function tests, thyroid function tests, urinalysis, and toxicology screening to rule out medical causes of psychosis. 1
First-Line Laboratory Tests
- Complete blood count (CBC): To identify infections and metabolic derangements
- Basic metabolic panel (BMP): To detect electrolyte abnormalities and metabolic disturbances
- Liver function tests (LFTs): To rule out liver dysfunction that may cause encephalopathy
- Thyroid function tests (TFTs): To identify thyroid disorders that can present with psychiatric symptoms
- Urinalysis: To detect urinary tract infections that may cause altered mental status
- Toxicology screening: To identify substance-induced psychosis, the most common medical cause of acute psychosis 2
Additional Tests to Consider
- Blood cultures: If patient is febrile to rule out infections
- HIV testing: To identify HIV-associated neurocognitive disorders
- Syphilis testing (RPR/VDRL): To rule out neurosyphilis
- Vitamin B12, folate, and niacin levels: To identify deficiencies that can cause psychiatric symptoms
- Calcium and parathyroid hormone: To detect metabolic disturbances
- Autoimmune panels: When autoimmune encephalitis is suspected
Red Flags Requiring More Extensive Workup
Pay special attention to patients with:
- Subacute onset of symptoms
- Recent head injury or trauma
- New or worsening headaches
- History of seizures
- Cerebrovascular disease
- Abnormal vital signs (tachycardia, hypertension, fever)
- Visual hallucinations (more common in medical causes)
- Age >65 years 1
- Focal neurological deficits
- Altered level of consciousness
Neuroimaging Considerations
Neuroimaging is not routinely required for all patients with new onset psychosis but should be considered when:
- Focal neurological deficits are present
- Abnormal neurological examination findings exist
- Atypical presentation or age of onset occurs
- First-episode psychosis without clear psychiatric cause
- New or worsening headaches
- History of head trauma 1
When indicated, head CT without IV contrast is typically the first-line neuroimaging test, though brain MRI may be preferred in certain clinical scenarios, particularly when the presentation is atypical or there are abnormal examination findings 3.
Clinical Pearls
- Medical causes are found in approximately 20% of patients with acute psychosis 4
- Patients with primary psychiatric disorders are more likely to have auditory hallucinations, while those with medical causes often have visual hallucinations 2
- Illicit drug use is the most common medical cause of acute psychosis 2
- Elderly patients require special attention as they are at higher risk of having abnormal brain imaging findings 1
- A subacute onset of psychosis should raise suspicion for an oncologic cause 2
Common Pitfalls to Avoid
- Failing to obtain collateral history from family members about the presentation and course of illness
- Overlooking vital sign abnormalities that may indicate medical causes (e.g., tachycardia or severe hypertension may indicate drug toxicity or thyrotoxicosis)
- Assuming psychosis is psychiatric in origin without ruling out medical causes
- Neglecting to perform a complete neurological examination
- Relying solely on routine laboratory tests without considering the clinical context
By following this systematic approach to laboratory evaluation, clinicians can effectively identify and address potential medical causes of new onset psychosis, which is critical for appropriate treatment and improved outcomes.