What laboratory tests should be ordered for a patient with postural tachycardia syndrome (POTS)?

Laboratory Tests for Postural Tachycardia Syndrome (POTS)

A comprehensive laboratory workup for POTS should include thyroid function tests, complete blood count, basic metabolic panel, and cardiac biomarkers to rule out secondary causes and guide treatment decisions. 1, 2

Core Laboratory Tests

• Complete blood count (CBC): Essential to evaluate for anemia which may contribute to orthostatic symptoms or exacerbate POTS 1
• Basic metabolic panel: To assess electrolyte abnormalities and renal function that may affect cardiovascular regulation 1
• Thyroid function tests: Thyroid disorders can mimic or exacerbate POTS symptoms and should be evaluated in all patients 3
• Glycohemoglobin (HbA1c): To screen for diabetes which can cause autonomic dysfunction 3

Cardiovascular Biomarkers

• Brain natriuretic peptide (BNP): May help identify cardiac causes of symptoms and assess for potential hypovolemic state 3, 1
• Serum electrolytes including calcium and magnesium: Important for cardiac conduction and muscle function 3
• Plasma norepinephrine levels: Can be elevated in hyperadrenergic POTS, particularly when measured in the upright position 2
• Renin-angiotensin-aldosterone profile: To evaluate for hypovolemia and abnormal sodium retention which are common in POTS 2

Additional Testing Based on Clinical Presentation

• Autoimmune markers: Consider in patients with suspected autoimmune-mediated POTS 4
• Plasma volume assessment: For evaluation of hypovolemia which is a common pathophysiological mechanism in POTS 2
• Catecholamine levels: May be elevated in hyperadrenergic POTS variants 5

Important Considerations

• Laboratory testing should be targeted based on clinical assessment rather than ordering comprehensive panels without specific indications 1
• Normal laboratory values do not exclude POTS diagnosis, as it is primarily a clinical and hemodynamic diagnosis 6, 7
• Laboratory abnormalities may guide treatment approaches (e.g., volume expansion for hypovolemic patients) 2
• Follow-up laboratory testing may be necessary to monitor treatment effects, particularly electrolytes if on medications affecting fluid balance 3

Diagnostic Algorithm

1. Initial laboratory evaluation: CBC, basic metabolic panel, thyroid function tests, and HbA1c 3, 1
2. Cardiovascular assessment: BNP, electrolytes including calcium and magnesium 3, 1
3. If hyperadrenergic features present: Add plasma catecholamines (supine and standing) 2
4. If hypovolemia suspected: Evaluate renin-angiotensin-aldosterone profile 2
5. If autoimmune features present: Consider autoimmune markers 4

Remember that laboratory testing is complementary to the primary diagnostic criteria for POTS, which requires an increase in heart rate of ≥30 bpm within 10 minutes of standing without orthostatic hypotension, along with characteristic symptoms persisting for at least 3 months 5, 7.