What labs are part of the workup for new onset psychosis?

Laboratory Workup for New Onset Psychosis

A comprehensive laboratory workup for new onset psychosis should include complete blood count, basic metabolic panel, liver function tests, thyroid function tests, urinalysis, and toxicology screening as first-line tests, with neuroimaging reserved for patients with atypical presentations, abnormal neurological findings, or specific risk factors.

First-Line Laboratory Tests

The initial laboratory workup for new onset psychosis should include:

• Complete blood count (CBC) - To rule out metabolic derangements and infections 1
• Basic metabolic panel (BMP) - To identify electrolyte abnormalities and metabolic disorders 1
• Liver function tests (LFTs) - To assess for liver dysfunction which can cause hepatic encephalopathy 1, 2
• Thyroid function tests (TSH, free T4) - To rule out thyroid disorders which can present with psychiatric symptoms 1, 2
• Urinalysis - To rule out urinary tract infections which can precipitate altered mental status, especially in elderly patients 1
• Urine toxicology screen - As illicit drug use is the most common medical cause of acute psychosis 2

Additional Laboratory Tests to Consider

Based on clinical presentation and risk factors, consider adding:

• Blood glucose - To rule out hypo/hyperglycemia
• Vitamin B12 and folate levels - Deficiencies can present with psychiatric symptoms 2
• Calcium and parathyroid hormone levels - To rule out hypercalcemia 2
• Niacin level - To rule out pellagra 2
• HIV testing - Especially in high-risk populations 2
• RPR/VDRL - To rule out neurosyphilis 2
• Blood cultures - If fever is present 1

Neuroimaging Considerations

Neuroimaging is not routinely required for all patients with new onset psychosis but should be considered in specific situations:

• Head CT without IV contrast is usually appropriate as the first-line neuroimaging test when indicated 3, 1
• Brain MRI may be preferred in certain clinical scenarios, particularly when the clinical picture is unclear, the presentation is atypical, or there are abnormal findings on examination 3

The yield of neuroimaging in detecting pathology responsible for psychotic symptoms is generally low (0-1.5%) in patients without neurological deficits 3.

Indications for Neuroimaging

Consider neuroimaging in patients with:

• Focal neurological deficits
• Abnormal neurological examination
• Atypical presentation or age of onset
• First-episode psychosis without clear psychiatric cause
• New or worsening headaches
• History of head trauma
• Suspected stroke, seizure, or intracranial infection
• Altered level of consciousness

Clinical Pearls and Pitfalls

• Medical causes are found in approximately 20% of patients with acute psychosis 4, highlighting the importance of a thorough medical workup
• Patients with primary psychiatric disorders typically present with auditory hallucinations, prominent cognitive disorders, and complicated delusions
• Patients with secondary (medical) psychosis may exhibit cognitive changes, abnormal vital signs, and visual hallucinations 2
• Red flags suggesting medical causes include:
  • Subacute onset (may suggest oncologic cause) 2
  • Recent head injury or trauma
  • New or worsening headaches
  • History of seizures
  • Cerebrovascular disease
  • Abnormal vital signs (fever, tachycardia, severe hypertension)
  • Visual (rather than auditory) hallucinations
  • Age >65 years (higher risk of medical causes) 3

Algorithmic Approach

1. Obtain first-line laboratory tests for all patients with new onset psychosis
2. Perform targeted additional testing based on clinical presentation and risk factors
3. Consider neuroimaging if atypical features or neurological abnormalities are present
4. Obtain collateral history from family members to establish presentation and course of illness
5. Perform complete neurological and mental status examinations

This approach balances the need to identify medical causes of psychosis while avoiding unnecessary testing that has a low diagnostic yield.