What laboratory tests are recommended for patients presenting with orthostatic hypotension?

Laboratory Tests for Orthostatic Hypotension

For patients presenting with orthostatic hypotension, a comprehensive laboratory evaluation should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, fasting blood glucose (glycohemoglobin), lipid profile, liver function tests, and thyroid-stimulating hormone. 1

Initial Laboratory Evaluation

The laboratory workup for orthostatic hypotension should focus on identifying potential underlying causes:

• Basic metabolic panel:

  • Serum electrolytes (sodium, potassium, calcium, magnesium)
  • Blood urea nitrogen (BUN)
  • Creatinine
  • Glucose

• Complete blood count (CBC):

  • To assess for anemia which can contribute to orthostatic symptoms

• Endocrine evaluation:

  • Thyroid-stimulating hormone (TSH)
  • Fasting blood glucose or glycohemoglobin (HbA1c) to screen for diabetes

• Liver function tests:

  • To assess for liver impairment that may affect medication metabolism 2

• Urinalysis:

  • To evaluate for renal disease or dehydration

• Lipid profile:

  • To assess cardiovascular risk factors

Additional Testing Based on Clinical Suspicion

Depending on the clinical presentation and suspected etiology, additional laboratory tests may be warranted:

• Renal function assessment:

  • Particularly important before initiating medications like midodrine, as renal impairment affects drug clearance 2

• Hepatic function assessment:

  • Liver has a role in midodrine metabolism, making hepatic function evaluation important before treatment 2

• Autonomic neuropathy workup:

  • For patients with diabetes or other conditions associated with autonomic dysfunction 1

Diagnostic Approach

The laboratory evaluation should be conducted alongside:

1. Orthostatic vital sign measurement:

   • Patient should lie down for 5 minutes before first measurement
   • Measurements taken after 1 and 3 minutes of standing
   • Patient should avoid caffeine, exercise, or smoking for 30 minutes before measurement 1

2. Medication review:

   • Identify medications that may cause or worsen orthostatic hypotension (antihypertensives, diuretics, tricyclic antidepressants, alpha-blockers, vasodilators) 1

Clinical Pearls and Pitfalls

• Pitfall: Failing to assess renal function before initiating treatment with medications like midodrine

  • Desglymidodrine (active metabolite of midodrine) is eliminated via the kidneys, and higher blood levels would be expected in patients with renal impairment 2

• Pitfall: Overlooking hepatic function assessment

  • The liver plays a role in midodrine metabolism, making hepatic function evaluation important 2

• Pearl: Consider cardiac causes of orthostatic symptoms

  • ECG should be performed to rule out cardiac causes of dizziness, especially with abnormal findings on physical exam 1

By following this systematic laboratory evaluation approach, clinicians can identify underlying causes of orthostatic hypotension and guide appropriate treatment decisions to improve patient outcomes.