What laboratory tests should be ordered to evaluate a patient presenting with panic attacks?

Laboratory Tests for Panic Attacks

Thyroid function tests (TSH, free T4) should be the primary laboratory test ordered for patients presenting with panic attacks, with additional testing guided by clinical presentation rather than routine extensive screening. 1

Evidence-Based Approach to Laboratory Testing

First-Line Testing

• Thyroid Function Tests: TSH and free T4 are recommended due to significant comorbidity between anxiety disorders and thyroid dysfunction 2, 1
  • Studies show thyroid disorders can present with or exacerbate anxiety symptoms
  • Female patients with panic disorder may have higher prevalence of thyroid dysfunction 2

Second-Line Testing (Based on Clinical Presentation)

• Complete Blood Count (CBC): To evaluate for anemia, infection, or other hematologic abnormalities that may contribute to anxiety symptoms 1
• Comprehensive Metabolic Panel (CMP): To assess electrolytes, glucose, kidney and liver function 1
  • Hypoglycemia can present with anxiety-like symptoms
  • Metabolic disturbances can worsen anxiety

Testing for Specific Clinical Presentations

When specific medical causes are suspected based on history and physical examination:

• For cardiovascular symptoms: Consider ECG (chest pain, tachycardia) 3
• For suspected pheochromocytoma: Plasma-free metanephrine or urinary vanillylmandelic acid 2, 4
• For suspected carcinoid syndrome: Serum serotonin or urinary 5-hydroxyindoleacetic acid 2
• For suspected hypoglycemia: Blood glucose testing 1

Evidence Against Routine Extensive Testing

The American College of Emergency Physicians recommends against routine extensive laboratory testing for psychiatric patients 2:

• Extensive, routine laboratory testing has been found unnecessary and potentially harmful
• False positive results are 8 times more frequent than true positives in routine testing 2
• Laboratory testing should be guided by the patient's clinical evaluation

Clinical Considerations and Pitfalls

Important Clinical Distinctions

• Distinguish panic attacks from vasodepressor (vasovagal) reactions:
  • Vasovagal reactions typically present with hypotension, pallor, weakness, nausea, vomiting, and diaphoresis
  • Panic attacks typically present with characteristic cutaneous manifestations and tachycardia 2

Common Pitfalls to Avoid

1. Overreliance on laboratory testing: Can lead to false positives and unnecessary follow-up testing 1
2. Missing medical causes: Conditions like hyperthyroidism, hypoglycemia, pheochromocytoma can manifest with anxiety-like symptoms 1, 4
3. Ignoring psychiatric comorbidities: Anxiety disorders commonly co-occur with depression and substance use disorders 1

Practical Algorithm for Laboratory Testing

1. For all patients with panic attacks:

   • Thyroid function tests (TSH, free T4)

2. For patients with specific presentations:

   • Cardiovascular symptoms: ECG
   • Episodic hypertension or flushing: Consider pheochromocytoma testing
   • Hypoglycemic symptoms: Blood glucose
   • Gastrointestinal symptoms: Consider CMP

3. For patients with atypical presentations or treatment resistance:

   • Consider more comprehensive testing based on specific clinical suspicion

Remember that panic disorder remains a clinical diagnosis, and laboratory testing serves primarily to rule out medical conditions that may mimic or exacerbate anxiety symptoms.