Plasma Norepinephrine Testing for POTS: What It Measures and Why It Matters

Plasma norepinephrine measurement — blood drawn while lying down and again after 10 minutes of standing — is one of the most important but underutilized tests in POTS evaluation. It is the definitive test for identifying hyperadrenergic POTS, the subtype that requires a fundamentally different treatment approach, and it provides valuable information about the degree of sympathetic nervous system activation in any POTS patient.

What Is Norepinephrine?

Norepinephrine (also called noradrenaline) is the primary neurotransmitter of the sympathetic nervous system. It is released by sympathetic nerve terminals throughout the body and by the adrenal medulla in response to stress, exercise, and orthostatic challenge (standing up).

When you stand up, baroreceptors detect the drop in blood pressure caused by gravitational blood pooling and trigger a sympathetic response. Norepinephrine is released to constrict blood vessels and increase heart rate, maintaining blood pressure. In POTS, this response is dysregulated — the heart rate increases excessively, and in hyperadrenergic POTS, norepinephrine levels surge far above normal.

Normal Values

Note: Reference ranges vary between laboratories. Always interpret results in the context of your specific lab's reference range.

How to Prepare for the Test

Medications to hold (confirm with your doctor):

• Beta-blockers: ideally hold for 5 half-lives before testing
• Clonidine and other sympatholytics: hold for 48 hours
• Tricyclic antidepressants: hold for 1 week (they block norepinephrine reuptake and will falsely elevate levels)
• SNRIs (venlafaxine, duloxetine): discuss with your doctor — they significantly affect norepinephrine levels

Day of the test:

• Avoid caffeine for 24 hours
• Avoid vigorous exercise for 24 hours
• Fast for 4 hours before the test (water is fine)
• Arrive early and rest supine for at least 20–30 minutes before the first blood draw

The test protocol:

1. An IV catheter is placed while you are lying down
2. You rest supine for 20–30 minutes
3. Blood is drawn for the supine norepinephrine level
4. You stand for exactly 10 minutes
5. Blood is drawn for the standing norepinephrine level

Interpreting Results

Standing norepinephrine ≥600 pg/mL: Diagnostic of hyperadrenergic POTS. This indicates excessive sympathetic activation on standing and should prompt a treatment approach focused on reducing sympathetic outflow (clonidine, low-dose beta-blockers) rather than volume expansion (fludrocortisone) or vasoconstrictors (midodrine).

Standing norepinephrine 200–600 pg/mL: Normal or mildly elevated. This is consistent with neuropathic or hypovolemic POTS subtypes. Does not rule out POTS — the diagnosis is based on heart rate criteria, not norepinephrine levels.

Supine norepinephrine >400 pg/mL: Elevated resting sympathetic tone, even before standing. This can indicate hyperadrenergic POTS, anxiety, pain, or other conditions causing chronic sympathetic activation.

Very high norepinephrine (>2000 pg/mL): Should prompt evaluation for pheochromocytoma (a rare adrenal tumor that secretes catecholamines). Pheo can mimic hyperadrenergic POTS and must be ruled out before treating with sympatholytics.

Why This Test Is Often Not Ordered

Despite its importance, plasma norepinephrine testing is not routinely ordered by most cardiologists and primary care physicians evaluating POTS. This is because:

1. POTS is diagnosed by heart rate criteria alone (no norepinephrine testing required)
2. Many physicians are not aware of the hyperadrenergic subtype or its treatment implications
3. The test requires careful protocol (supine rest, timed standing) that is not always feasible in a busy clinic

If you suspect hyperadrenergic POTS based on your symptoms (blood pressure rises on standing, tremor, profuse sweating, anxiety-like episodes, worsening with beta-blockers), specifically request plasma norepinephrine testing with both supine and standing samples.