What labs should be drawn when someone is hallucinating?

Laboratory Evaluation for Hallucinations

When evaluating a patient with hallucinations, obtain a targeted laboratory panel based on clinical presentation rather than reflexive comprehensive testing, prioritizing glucose, basic metabolic panel, complete blood count, thyroid function, and urine toxicology as first-line tests, with additional studies guided by specific risk factors identified on history and physical examination. 1, 2

Initial Risk Stratification

The clinical presentation determines the extent of laboratory evaluation needed:

• Check vital signs immediately as tachycardia, fever, hypertension, or hypotension suggest organic causes requiring more extensive metabolic workup 1
• Assess for altered mental status, fever, or focal neurological deficits, as these findings mandate broader evaluation regardless of presentation 1
• Evaluate cognitive function since disorientation or confusion indicates possible delirium and necessitates comprehensive metabolic testing 1
• Identify high-risk populations including elderly patients, those without prior psychiatric history, patients with substance abuse history, and those with new medical complaints—these groups require more thorough laboratory evaluation 1

Core Laboratory Panel (Tier 1)

These tests should be obtained in most patients presenting with hallucinations:

• Serum glucose to exclude hypoglycemia or hyperglycemia, particularly if there is any suspicion based on history or examination 1, 2
• Complete blood count (CBC) when infection is suspected based on fever, leukocytosis risk factors, or immunocompromised status 1, 2
• Basic metabolic panel including electrolytes, BUN, and creatinine in patients with known renal disease, medications affecting electrolytes, or clinical signs of metabolic derangement 1, 2
• Thyroid function tests (TSH) as part of the initial evaluation for new-onset psychotic symptoms 2
• Urine toxicology screen given that illicit drug use is the most common medical cause of acute psychosis 2, 3

Additional Testing Based on Clinical Indicators

Expand the laboratory evaluation when specific risk factors are present:

• Serum calcium and magnesium if hypocalcemia or hypomagnesemia is suspected based on medication use, renal disease, or alcoholism 4, 2
• Liver function tests in patients with known liver disease or alcohol abuse 2
• Vitamin B12, folate, and niacin levels particularly in older adults with cognitive changes or nutritional deficiencies 2
• HIV testing and syphilis serology (RPR or VDRL) should be considered based on risk factors 4, 2
• Parathyroid hormone (PTH) if calcium abnormalities are detected 2

Special Population Considerations

Elderly Patients

• Lower threshold for checking electrolytes, particularly sodium and calcium, due to higher risk of organic causes 1
• Vitamin B12 and folate levels should be routinely considered 1
• Medication review is critical as polypharmacy commonly causes hallucinations in this population 1

Children and Adolescents

• All children and adolescents with psychotic symptoms should receive thorough pediatric and neurological evaluation 4
• Basic laboratory tests include CBC, serum chemistry studies, thyroid function, urinalysis, and toxicology screens 4
• Toxicology screens are particularly appropriate given high rates of substance abuse in this age group 1
• HIV testing if risk factors are present 4
• Chromosomal analysis may be indicated for patients with clinical features suggestive of developmental syndromes like velocardiofacial syndrome 4

Substance Use History

• Comprehensive urine toxicology is essential, as substance-induced psychosis is common 4, 2
• If psychotic symptoms persist longer than one week despite documented detoxification, consider primary psychotic disorder rather than substance-induced psychosis 4

Neuroimaging and Advanced Testing

Consider these studies based on specific clinical findings:

• Brain MRI (or CT if MRI unavailable/contraindicated) when there is history of head trauma, new or worsening headaches, focal neurological signs, or first-episode psychosis 4, 2
• EEG if seizure disorder is suspected based on history or examination 4
• Lumbar puncture with CSF analysis if CNS infection (encephalitis, meningitis) is suspected, particularly in febrile patients or immunocompromised individuals 4

Critical Pitfalls to Avoid

• Do not order extensive routine laboratory panels reflexively—history and physical examination predict 83-98% of clinically significant abnormalities 1
• Never assume psychiatric etiology without excluding medical causes in high-risk groups such as elderly patients, first presentation, abnormal vital signs, or substance abuse history 1
• Do not rely solely on immunoassay-based toxicology screens as they have limitations in sensitivity and specificity; consider confirmatory testing when clinical suspicion is high 3
• Avoid labeling patients with "withdrawal seizures" or substance-induced hallucinations before eliminating symptomatic causes 4
• Remember that organic psychosis must be considered when obtaining history, completing physical examination, and selecting laboratory investigations, as the list of potential etiologies is extensive including delirium, seizures, CNS lesions, metabolic disorders, toxic encephalopathies, and infectious diseases 4