In a 30‑year‑old woman with chronic fatigue, orthostatic dizziness, palpitations, exercise intolerance, heat intolerance, normal thyroid function tests and normal basic metabolic panel, and an orthostatic blood‑pressure drop of less than 15 mm Hg, what further diagnostic workup is indicated?

Workup for Suspected Postural Orthostatic Tachycardia Syndrome (POTS)

This clinical presentation strongly suggests POTS, and you should proceed with a formal 10-minute active stand test with continuous heart rate and blood pressure monitoring at baseline supine, immediately upon standing, and at 2,5, and 10 minutes to confirm the diagnosis. 1, 2

Why POTS is the Leading Diagnosis

Your patient's constellation of symptoms—chronic fatigue, orthostatic dizziness, palpitations, exercise intolerance, and heat intolerance—precisely matches the clinical profile of POTS, which predominantly affects young women and presents with severe orthostatic intolerance triggered by standing. 3 The key diagnostic clue is that her orthostatic vital signs showed less than a 15 mmHg blood pressure drop, which rules out orthostatic hypotension (which requires ≥20 mmHg systolic or ≥10 mmHg diastolic drop) but does not exclude POTS. 1, 2 POTS is specifically defined by excessive heart rate increase (≥30 bpm within 10 minutes of standing) without meeting criteria for orthostatic hypotension. 1, 3

The Formal Diagnostic Stand Test Protocol

Pre-Test Preparation

• Have the patient fast for 4 hours prior to testing to ensure accurate results. 2
• Avoid stimulants (caffeine, nicotine) and maintain a controlled room temperature. 2
• Review all medications, as certain drugs can confound results. 2

Testing Procedure

• Measure baseline heart rate and blood pressure after the patient lies supine for 5 minutes. 2
• Have the patient stand quietly (non-exertional standing) and immediately record heart rate and blood pressure. 2
• Continue recording at 2,5, and 10 minutes of standing. 2
• Diagnostic threshold: A sustained heart rate increase of ≥30 bpm (or heart rate >120 bpm) within 10 minutes, without orthostatic hypotension, confirms POTS. 1, 2, 3

Critical Testing Pitfalls to Avoid

• Do not stop the test prematurely—the full 10 minutes is essential, as some patients develop tachycardia later in the stand period. 2
• Do not dismiss POTS simply because the standing heart rate doesn't exceed 120 bpm; the ≥30 bpm increase from baseline is sufficient. 2
• Ensure you document that orthostatic hypotension criteria are not met, as this distinction is crucial. 2

Essential Baseline Laboratory and Cardiac Workup

Even though thyroid function and basic metabolic panel are normal, complete the following to exclude mimics and identify associated conditions:

Mandatory Tests

• 12-lead ECG to rule out arrhythmias, conduction abnormalities, or inappropriate sinus tachycardia. 2
• Complete blood count to exclude anemia as a cause of tachycardia and fatigue. 3
• Comprehensive medication review to identify drugs that may contribute (diuretics, vasodilators, antidepressants). 2

Strongly Recommended Screening

• Beighton score assessment for joint hypermobility syndrome, as POTS frequently coexists with hypermobile Ehlers-Danlos syndrome, particularly in young women with chronic fatigue and orthostatic intolerance. 3, 4 This association is well-documented: abnormal connective tissue in dependent blood vessels permits excessive venous distension and pooling, leading to the hemodynamic consequences of POTS. 4
• Document the duration and pattern of fatigue to evaluate for chronic fatigue syndrome, which co-occurs with orthostatic intolerance in up to 72% of cases when standing. 5, 6

Alternative Testing if Stand Test is Inconclusive

If the active stand test yields equivocal results or the patient cannot tolerate standing for 10 minutes, perform a head-up tilt-table test at ≥60 degrees for up to 10 minutes. 2 This is particularly useful when standard orthostatic vital signs are nondiagnostic. 7

Understanding the Symptom Pattern

The symptoms you describe—dizziness, palpitations, exercise intolerance, heat intolerance, and fatigue that worsen with standing—are the cardinal features of orthostatic intolerance and are relieved by sitting or lying down. 1, 3 Importantly, research shows that 41% of CFS patients have symptoms even while recumbent, and this increases to 72% when standing, so the presence of symptoms at rest does not exclude POTS. 5 Heat intolerance and postexertional malaise are common exacerbating factors in POTS. 3

What You've Already Ruled Out

• Orthostatic hypotension: The <15 mmHg blood pressure change excludes classic orthostatic hypotension, which requires ≥20 mmHg systolic or ≥10 mmHg diastolic drop. 1, 7
• Thyroid dysfunction: Normal thyroid function tests exclude hyperthyroidism as a cause of tachycardia and heat intolerance. 2
• Metabolic derangements: Normal CMP excludes electrolyte abnormalities, renal dysfunction, and glucose disorders. 2

Next Steps After Diagnosis

If POTS is confirmed, first-line management includes a gradual exercise reconditioning program, increased salt intake (8–10 grams daily), fluid intake (2–3 liters daily), and compression garments (waist-high, 30–40 mmHg). 1 Patient education on recognizing triggers (prolonged standing, heat, dehydration, large meals) and physical counterpressure maneuvers (leg crossing, muscle tensing) is essential. 1