What lab values can explain psychosis?

Laboratory Evaluation for Psychosis

Laboratory testing for psychosis should be guided by clinical presentation rather than routine screening, with essential initial tests including complete blood count, comprehensive metabolic panel, thyroid function tests, urinalysis, and toxicology screens. 1

Core Laboratory Panel

The following tests should be considered as part of the basic medical evaluation when psychosis is present:

• Complete blood count (CBC) to evaluate for anemia or infection that could contribute to altered mental status 1, 2
• Comprehensive metabolic panel including electrolytes, renal function (BUN/creatinine), glucose, and liver function to assess for metabolic derangements, acid-base disturbances, and organ dysfunction 1, 2, 3
• Thyroid function tests (TSH, free T4) to rule out hyperthyroidism or hypothyroidism, both of which can present with psychotic symptoms 1, 2, 3
• Urinalysis to screen for urinary tract infections and metabolic abnormalities 1
• Urine toxicology screen given that illicit drug use is the most common medical cause of acute psychosis 1, 3

Additional Testing Based on Clinical Context

When history or physical examination suggests specific etiologies, expand testing to include:

• Calcium and parathyroid hormone (PTH) to evaluate for hypercalcemia and hyperparathyroidism 3
• Vitamin B12, folate, and niacin levels to assess for nutritional deficiencies that can cause psychosis 3
• HIV testing if risk factors are present, as HIV-related syndromes can manifest with psychotic symptoms 1, 3
• Syphilis testing (RPR/VDRL) should be considered as neurosyphilis can present with psychiatric manifestations 3
• Cardiac enzymes if cardiac injury is suspected clinically 2
• Ceruloplasmin and 24-hour urine copper if Wilson's disease is suspected (particularly in younger patients with movement disorders) 1

High-Risk Populations Requiring More Extensive Workup

Certain patient groups warrant lower thresholds for laboratory investigation:

• Elderly patients presenting with new-onset psychosis 1
• Patients with substance abuse history (up to 50% comorbidity in adolescents with schizophrenia) 1
• Patients without prior psychiatric history presenting with first-episode psychosis 1, 3
• Patients with preexisting or new medical complaints 1
• Lower socioeconomic populations 1

Clinical Indicators Suggesting Medical Etiology

Laboratory abnormalities are more likely to explain psychosis when accompanied by:

• Abnormal vital signs including fever (suggesting encephalitis, porphyria), tachycardia, or severe hypertension (suggesting drug toxicity or thyrotoxicosis) 1, 3
• Altered level of consciousness or cognitive changes (unlike primary psychosis where awareness is typically intact) 1, 4, 3
• Visual hallucinations (more common in medical causes versus auditory hallucinations in primary psychiatric disorders) 3
• Acute or subacute onset particularly in patients over age 40 or under age 12 3
• Abnormal neurological examination 1

Critical Pitfalls to Avoid

Do not order extensive routine laboratory batteries in alert, cooperative patients with normal vital signs and noncontributory history and physical examination. 1 Studies demonstrate that false positive results are 8 times more frequent than true positives (1.8%) when routine testing is performed without clinical indication 1. This approach is costly, low-yield, and unlikely to affect disposition or management 1.

However, maintain high suspicion in specific scenarios: Up to 46% of patients with psychiatric symptoms may have medical illnesses directly causing or exacerbating their presentation 2. In one study of patients with new psychiatric complaints, 63% had a medical reason for their behavior, though this included many patients with delirium and abnormal vital signs 1.

Substance-Induced Psychosis Considerations

When substance use is identified:

• Persistent psychotic symptoms beyond one week despite documented detoxification suggest a primary psychotic disorder rather than substance-induced psychosis 1
• Illicit drugs (amphetamines, cocaine, hallucinogens, PCP, marijuana, synthetic cannabinoids, cathinones) are the most common medical cause of acute psychosis 1, 3, 5
• Medications including stimulants, corticosteroids, and anticholinergic agents can induce psychosis 1

Timing and Interpretation

Laboratory testing should be justified based on clinical presentation and significant findings in history or physical examination 1. The decision about what constitutes an "important" positive finding should be guided by whether it changes management or explains the psychotic presentation 1. Longitudinal reassessment may be necessary, as diagnostic accuracy improves over time 1.