What baseline laboratory tests are recommended for an adult before a psychiatric evaluation and initiation of psychotropic medication?

Baseline Laboratory Testing for Psychiatric Evaluation

For alert, cooperative adults with normal vital signs and a noncontributory history and physical examination presenting for psychiatric evaluation, routine laboratory testing is not indicated—diagnostic evaluation should be directed by clinical findings from history and physical examination only. 1

Core Principle: History-Driven Testing, Not Reflexive Panels

• History alone has 94% sensitivity for identifying medical conditions in psychiatric patients, while laboratory studies alone have only 20% sensitivity. 1, 2
• Routine laboratory panels yield false positive results 8 times more often than true positives when performed without clinical indication. 2
• Only 4% of psychiatric patients required acute medical treatment within 24 hours of admission, and in 83% of these cases, history and physical examination were sufficient to identify the problem. 1

High-Risk Populations Requiring Lower Testing Thresholds

Order targeted laboratory studies in these four groups: 2

• Elderly patients (≥65 years) 2
• Patients with substance abuse history 2
• First psychiatric presentation 2
• New or preexisting medical complaints 2

Specific Clinical Triggers for Laboratory Testing

Vital Sign Abnormalities

• Fever: Check complete blood count and consider infectious workup 2
• Tachycardia: Obtain ECG, assess for medication effects, evaluate for QT prolongation 2
• Hypertension or hypotension: Check electrolytes and renal function 2

Mental Status Changes

• Altered mental status or disorientation: Order comprehensive metabolic panel and consider hyperammonemia workup 2

Medical Comorbidities

• Diabetes: Check glucose if altered mental status, new psychiatric symptoms, or medication changes present 2
• Hypertension on diuretics or ACE inhibitors: Monitor blood pressure and check electrolytes 2

Substance Use Considerations

• Chronic alcohol use: Check electrolytes for complications 2
• Stimulant use: Perform cardiac monitoring 2

Medication-Specific Baseline Requirements

Before Initiating Antipsychotics

• Obtain ECG to assess for QT prolongation 2
• Check metabolic syndrome parameters 2

Before Initiating Valproate

• Baseline platelet count 2
• Coagulation parameters 2
• Liver function tests 2

Before Initiating Carbamazepine or Oxcarbazepine

• Test for HLA-A and HLA-B due to risk of serious skin reactions 3

What NOT to Order

Urine Drug Screening

• Routine urine toxicology screening is not indicated and should only be ordered when results would change acute management or disposition. 1, 2
• Studies show no difference in patient disposition or hospital length of stay between mandatory urine drug screening versus usual care. 1
• Urine drug screens have only 20% sensitivity for organic etiology of psychiatric complaints. 1

Routine Laboratory Panels

• Avoid ordering CBC, comprehensive metabolic panels, or other routine batteries without specific clinical indication. 1, 2, 4
• The prevalence of clinically significant laboratory results that change disposition ranges from 0.0% to 0.4% when routine testing is performed. 4

Neurologic Red Flags Requiring Broader Evaluation

Order comprehensive workup including neuroimaging when: 2

• Focal neurological deficits present
• First seizure or new seizure pattern
• Head trauma history with behavioral change
• Signs of increased intracranial pressure
• Acute stroke symptoms

Critical Pitfalls to Avoid

• Never assume psychiatric etiology without excluding organic causes in high-risk groups (elderly, substance abuse, first presentation, medical complaints). 2
• Never dismiss tachycardia as "anxiety" without structured cardiac assessment including ECG. 2
• Ordering extensive panels reflexively leads to false positives and unnecessary workup that can harm patients. 2
• In patients with new psychiatric symptoms (not previously diagnosed psychiatric illness), 63% have an organic etiology requiring more extensive evaluation. 5