What laboratory tests should be ordered for a patient experiencing their first psychotic episode?

Laboratory Tests for First Psychotic Episode

For a patient experiencing their first psychotic episode, essential laboratory tests should include complete blood count, comprehensive metabolic panel, thyroid function tests, urinalysis, and toxicology screen to rule out medical causes of psychosis that could affect morbidity and mortality. 1, 2

Core Laboratory Tests

First-Line Tests (Essential)

• Complete blood count (CBC)
• Comprehensive metabolic panel/serum chemistry studies
• Thyroid function tests
• Urinalysis
• Toxicology screen (urine and/or serum)

Second-Line Tests (Based on Clinical Suspicion)

• HIV testing (if risk factors present)
• RPR/VDRL for syphilis
• Vitamin B12 and folate levels
• Calcium and parathyroid hormone levels
• Ammonia levels (if hepatic encephalopathy suspected)

Rationale for Testing

Laboratory tests in first-episode psychosis serve two critical purposes:

1. Rule out organic/medical causes of psychotic symptoms
2. Establish baseline values before initiating antipsychotic medications

The American Academy of Child and Adolescent Psychiatry emphasizes that laboratory tests are not used to diagnose schizophrenia but rather to exclude other neurological or medical problems that could present with psychotic symptoms 1. This is crucial as up to 46% of patients with psychotic symptoms may have medical illnesses directly causing or exacerbating their psychiatric presentation 1.

Medical Conditions to Consider

When evaluating first-episode psychosis, consider these potential medical causes:

• Delirium
• Seizure disorders
• CNS lesions (tumors, trauma)
• Neurodegenerative disorders
• Metabolic disorders (endocrinopathies, Wilson's disease)
• Developmental disorders
• Toxic encephalopathies (substance-induced)
• Infectious diseases (encephalitis, meningitis, HIV)
• Thyroid disorders 1, 2, 3

Special Considerations

Substance Use

Given the high comorbidity of substance abuse in patients with psychosis (up to 50%), toxicology screening is particularly important 1. If psychotic symptoms persist for longer than a week despite documented detoxification, consider a primary psychotic disorder rather than substance-induced psychosis.

Neuroimaging

While not a laboratory test, neuroimaging (CT or MRI) should be considered for patients with:

• Focal neurological deficits
• New or worsening headaches
• History of head trauma
• Atypical presentation or age of onset
• First-episode psychosis without clear psychiatric cause 2

Age-Specific Considerations

For elderly patients with new-onset psychosis, additional testing for B12 deficiency should be considered 2.

Common Pitfalls to Avoid

1. Premature psychiatric diagnosis: Avoid attributing psychotic symptoms to a psychiatric disorder without adequate medical workup
2. Overlooking substance use: Substance-induced psychosis is common but often missed
3. Incomplete testing: Failing to perform basic laboratory tests before neuroimaging
4. Missing atypical presentations: Infections and metabolic disorders can present atypically, especially in elderly patients 2, 3

By following this systematic approach to laboratory testing in first-episode psychosis, clinicians can effectively rule out medical causes that could significantly impact patient morbidity and mortality while establishing important baseline values before initiating treatment.