What labs should be ordered for a 34-year-old transgender male with a history of back pain, substance use disorder, major depressive disorder, and testosterone (hormone) therapy, presenting with tunnel vision and loss of consciousness?

Diagnostic Workup for Syncope in a Transgender Male with Multiple Risk Factors

Initial Assessment and Priority Testing

For a transgender male with tunnel vision and loss of consciousness, a focused cardiovascular and neurological workup is essential, with specific attention to testosterone therapy effects, substance use history, and metabolic factors.

The presentation of syncope (loss of consciousness) with prodromal tunnel vision in this 34-year-old transgender male requires a systematic approach to identify the underlying cause. Given the patient's complex medical history including testosterone therapy, substance use disorder, and major depressive disorder, several diagnostic pathways must be explored.

First-Line Laboratory Tests

1. Cardiovascular Assessment:

   • 12-lead ECG (to assess for arrhythmias, QT prolongation, and structural abnormalities) 1
   • Orthostatic vital signs (blood pressure and heart rate measurements lying, sitting, and standing)
   • Troponin levels (to rule out cardiac ischemia)
   • BNP or NT-proBNP (to assess for heart failure)

2. Neurological Assessment:

   • Complete blood count (to rule out anemia or infection)
   • Electrolytes, BUN, creatinine (to assess for metabolic derangements)
   • Calcium, magnesium, phosphorus (for electrolyte abnormalities that can cause neurological symptoms) 1, 2

3. Endocrine Assessment:

   • Testosterone levels (both total and free testosterone)
   • Estradiol levels (to assess hormone balance)
   • Thyroid function tests (TSH, free T4) 2
   • Cortisol level (morning) to rule out adrenal insufficiency

4. Toxicology and Substance Use:

   • Comprehensive urine drug screen (including alcohol, opioids, benzodiazepines, stimulants) 1, 2
   • Blood alcohol level
   • Liver function tests (to assess for liver dysfunction from alcohol use disorder) 2

Second-Line Testing

1. Neuroimaging:

   • Head CT without contrast (if there are focal neurological findings, atypical presentation, or concern for intracranial pathology) 2
   • Consider MRI brain if CT is negative but clinical suspicion remains high for neurological etiology

2. Extended Cardiac Evaluation:

   • Echocardiogram (to assess structural heart disease and ejection fraction)
   • Consider Holter or event monitor for intermittent arrhythmias
   • Tilt-table testing if vasovagal syncope is suspected 1

3. Additional Laboratory Tests:

   • Hemoglobin A1c was already checked (5.5%) and glucose (108 mg/dL), ruling out diabetes as a primary cause
   • Prolactin level (can be affected by certain medications and psychiatric conditions)
   • Consider EEG if seizure activity is suspected 1

Clinical Considerations and Rationale

Testosterone Therapy Considerations

Testosterone therapy in transgender males can increase risk of:

• Polycythemia (check hematocrit)
• Cardiovascular events including arrhythmias
• Mood disturbances that may exacerbate underlying psychiatric conditions 3

Substance Use Considerations

• Alcohol use disorder can cause:
  • Hypoglycemia (though glucose is normal in this case)
  • Electrolyte abnormalities
  • Withdrawal syndromes
  • Wernicke-Korsakoff syndrome (check thiamine level) 2
  • Liver dysfunction affecting medication metabolism

Psychiatric Medication Considerations

• Many psychiatric medications can cause:
  • Orthostatic hypotension
  • QT prolongation
  • Electrolyte abnormalities
  • Serotonin syndrome (if on multiple serotonergic agents)

Common Pitfalls to Avoid

1. Don't attribute syncope to psychiatric causes without ruling out organic etiologies - Psychiatric diagnoses are diagnoses of exclusion when evaluating syncope 1, 2

2. Don't overlook medication interactions - Testosterone may interact with psychiatric medications or substances of abuse

3. Don't miss cardiac causes - Cardiovascular causes of syncope have higher mortality rates and require prompt identification 4, 5

4. Don't forget to consider neurological causes - Cerebrovascular events can present with transient loss of consciousness and are more common in patients with substance use disorders 5

5. Don't neglect the impact of hormone therapy - Testosterone therapy can affect multiple organ systems and contribute to syncope through various mechanisms

Summary of Key Laboratory Tests

The most critical laboratory tests to order in this case are:

• 12-lead ECG
• Complete blood count
• Comprehensive metabolic panel
• Testosterone levels (total and free)
• Thyroid function tests
• Urine drug screen
• Liver function tests
• Consider head CT if neurological findings are present

This targeted approach will help identify the most likely causes of syncope in this complex patient with multiple risk factors while avoiding unnecessary testing.