Norepinephrine
Overview
Norepinephrine measures a catecholamine neurotransmitter and hormone synthesized in sympathetic nerve terminals and the adrenal medulla that mediates the fight-or-flight response through α- and β-adrenergic receptor activation. It increases heart rate, blood pressure, and vascular tone while redirecting blood flow to vital organs during stress. Elevated levels indicate pheochromocytoma, sympathetic overactivity, or critical illness; low levels suggest autonomic failure or adrenal insufficiency. Clinically, plasma norepinephrine testing evaluates autonomic disorders, hypertensive crises, and shock states.
Clinical Use Cases
- Diagnosing pheochromocytoma and paraganglioma.
- Evaluating orthostatic hypotension and autonomic dysfunction.
- Assessing septic shock and catecholamine-resistant hypotension.
- Monitoring chronic heart failure and essential hypertension pathophysiology.
Specimen Types
- Plasma (EDTA with reduced glutathione antioxidant).
- Whole blood (for fractionated catecholamines).
- Urine (24-hour collection for metanephrine correlation).
Measurement Methods
- High-performance liquid chromatography with electrochemical detection (HPLC-ECD).
- Tandem mass spectrometry (LC-MS/MS).
- Radioenzymatic assay (legacy method).
Test Preparation and Influencing Factors
- Patient supine 30 minutes prior to collection; acute stress elevates levels.
- Avoid caffeine, bananas, and vanillin-containing foods for 48 hours.
- Tricyclic antidepressants, levodopa, and sympathomimetics interfere.
- Sample must remain cold; immediate acidification for urine prevents degradation.
Synonyms
- Noradrenaline.
- Levonordefrin.