TABLE 2.

Laboratory Evaluation in Patients With POTS

Investigation	Rationale
Cardiac evaluation (ECG, echocardiogram, Holter monitoring)	Exclude a primary cardiac cause of inappropriate sinus tachycardia
Head-up tilt (at a 60° angle for 10 min)	Distinguish POTS from other forms of OI
Cardiovagal and sudomotor function tests	Detect underlying autonomic neuropathy
Plasma catecholamine, both supine and during standing or head-up tilt	Assessment of baroreflex sympathoexcitation and possible hyperadrenergic POTS
24-Hour blood pressure and heart rate monitoring	Correlate the timing of the patient's symptoms with the presence of tachycardia
Exercise testing with V̇o2max	Detect physical deconditioning
Additional tests in individual cases am and pm cortisol  Thyroid cascade   Plasma and urinary metanephrines  Serum tryptase, urinary methylhistamine  Autoantibodies (VGKC complex, ganglionic AChR)  MRI of the head with gadolinium	Evaluate for chronic fatigue Evaluate for hyperadrenergic state Detect pheochromocytoma Detect mast cell activation disorders Detect autoimmune causes of POTS Patients with orthostatic headache
Special additional evaluations
Gastrointestinal or urologic evaluations	POTS patients with suspected functional visceral dysmotility syndromes
Behavioral medicine evaluation	POTS patients with multiple associated nonorthostatic symptoms

AChR = acetylcholine receptor; ECG = electrocardiogram; MRI = magnetic resonance imaging; OI = orthostatic intolerance; POTS = postural tachycardia syndrome; VGKC = voltage-gated potassium channel.