Endocrinology & Clinical Biochemistry
Urinary catecholamines — Epinephrine, norepinephrine, dopamine
Catecholamines are a group of neurotransmitters and hormones derived from tyrosine—primarily adrenaline (epinephrine), noradrenaline (norepinephrine), and dopamine—synthesized by the chromaffin cells of the adrenal medulla (adrenaline at 80% %, noradrenaline at 20%), by postganglionic sympathetic nerve endings (mainly noradrenaline), and by dopaminergic neurons in the central nervous system. The biological assessment of catecholamines is based on the measurement of these molecules and their metabolites in 24-hour urine or plasma. The main urinary metabolites measured are metanephrines (direct metabolites of epinephrine and norepinephrine via catechol-O-methyltransferase—COMT) and vanillylmandelic acid (VMA) (a common terminal metabolite following the action of COMT and monoamine oxidase—MAO). Dopamine is excreted in the form of its own metabolites—notably homovanillic acid (HVA). The primary indication for measuring urinary catecholamines is the screening and diagnosis of pheochromocytoma and secreting paraganglioma—rare tumors of the chromaffin cells of the adrenal medulla (pheo) or the para-aortic sympathetic ganglia (paraganglioma) responsible for catecholamine hypersecretion, secondary hypertension (often paroxysmal), and potentially fatal hypertensive crises if undiagnosed. Neuroblastoma—a malignant tumor of the sympathetic nervous system in children—is another major indication, with a characteristic elevation of urinary catecholamines (particularly HVA and VMA) that serves both diagnostic and therapeutic monitoring purposes. Fractionated plasma metanephrines (free) are now recognized as the most sensitive first-line test for pheochromocytoma (sensitivity 97–99% %), with fractionated urinary metanephrines (sensitivity 90–97% %) as the preferred alternative; measurement of free urinary catecholamines (adrenaline, noradrenaline) is less sensitive but can provide additional information on the secretion profile.
Biosynthesis and metabolism of catecholamines
- Synthesis pathway (Blaschko's cascade): tyrosine (dietary amino acid or synthesized from phenylalanine) → DOPA (dihydroxyphenylalanine) by tyrosine hydroxylase (rate-limiting enzyme, feedback inhibited) → dopamine by DOPA decarboxylase (aromatic L-amino acid decarboxylase) → norepinephrine by dopamine beta-hydroxylase (DBH) in storage vesicles → epinephrine by phenylethanolamine N-methyltransferase (PNMT) - enzyme expressed only in the adrenal medulla, induced by glucocorticoids; epinephrine biosynthesis therefore requires direct anatomical proximity between the adrenal cortex (glucocorticoids) and the adrenal medulla (chromaffin cells)
- Catabolism and measurable metabolites: Catecholamines are metabolized by two main enzymes—catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO); COMT (cytoplasmic, intracellular) converts adrenaline to metanephrine and noradrenaline to normetanephrine—this conversion occurs continuously within the tumor cells (chromaffin cells) of pheochromocytomas themselves, independently of secretion episodes, which is why metanephrines are more stable and sensitive markers than free catecholamines; MAO (mitochondrial) degrades catecholamines into aldehydes → MHPG (3-methoxy-4-hydroxyphenylglycol) and VMA (vanillylmandelic acid = terminal metabolite of adrenaline and noradrenaline); dopamine → HVA (homovanillic acid) via MAO + COMT
- Very short plasma half-life: adrenaline 1–2 minutes, noradrenaline 2–3 minutes → marked instability of free plasma catecholamines (sensitive to the stress of blood draw, standing, smoking, caffeine) → justifies the superiority of metanephrines (stable intracellular metabolites with a longer half-life) for the biological diagnosis of pheochromocytoma
24-hour urine reference values
| Analyst | Adult normal values | Remarks |
|---|---|---|
| Adrenaline (epinephrine) | < 100 nmol/24 h (< 18 µg/24 h) |
Secreted almost exclusively by the adrenal medulla; isolated elevation highly suggestive of adrenal pheochromocytoma; values vary by laboratory (HPLC or LC-MS/MS method) |
| Norepinephrine | < 570 nmol/24 h (< 97 mcg/24 h) |
Produced by the adrenal medulla and by peripheral sympathetic nerve endings; higher than adrenaline at the basal state; preferential elevation in extra-adrenal paragangliomas and norepinephrine-secreting pheochromocytomas (mutated SDHB) |
| Dopamine | < 3,000 nmol/24 h (< 460 µg/24 h) |
Strongly influenced by diet (banana, pineapple, nuts); elevated in neuroblastomas, dopaminergic pheochromocytomas (rare - SDHB/SDHD mutations) and certain head and neck paragangliomas; to be interpreted in conjunction with dietary intake |
| Vanillylmandelic acid (VMA) | Less than 35 micromoles per 24 hours (< 7 mg/24 h) |
Common terminal metabolite of adrenaline and noradrenaline; an older colorimetric method (less specific—numerous dietary interferences) has been progressively replaced by fractionated metanephrines by LC-MS/MS in modern laboratories; still requested in current practice for neuroblastoma |
| Fractionated urinary metanephrine | < 1,200 nmol/24 h (< 220 mcg/24 h) |
Adrenaline metabolite — most specific marker for adrenal pheochromocytoma; assay by LC-MS/MS (reference method); minimally influenced by stress or diet (stable intracellular metabolite) |
| Fractionated urinary normetanephrine | < 3100 nmol/24 h (< 570 µg/24 h) |
Norepinephrine metabolite—elevated in norepinephrine-dominant pheochromocytomas and paragangliomas; slightly higher sensitivity than metanephrine for detection of extra-adrenal paragangliomas |
| Homovanillic acid (HVA) | < 36 µmol/24h (< 7 mg/24 h) |
Terminal metabolite of dopamine; elevated in neuroblastomas (often associated with elevated VMA) and in dopaminergic pheochromocytomas (rare); influenced by diet rich in dopamine precursors |
ℹ️
Reference values vary depending on the laboratory and the analytical method used (fluorimetric HPLC, LC-MS/MS — liquid chromatography coupled to tandem mass spectrometry). Results should always be interpreted in conjunction with the reference values specific to the laboratory that performed the analysis. The LC-MS/MS method is currently the reference method for the assay of fractionated metanephrines, offering the best analytical specificity with the fewest drug and food interferences.
Main causes of elevation
| Cause | Biological mechanism and characteristics |
|---|---|
| Pheochromocytoma | Adrenomedullary chromaffin cell tumor — secretes excess epinephrine and/or norepinephrine; elevated fractional metanephrines in >95% of cases; levels typically >3 to 4 times the upper limit of normal — strongly suggestive of malignancy below this threshold; 10% malignant, 10% bilateral, 10% extra-adrenal, 10% familial (the “rule of 10%”—now outdated: 25–40% associated with a germline mutation); mutations: SDHB (malignant paraganglioma), SDHD, VHL (Von Hippel-Lindau disease), NF1 (neurofibromatosis type 1), RET (NEM2A and NEM2B), MAX, TMEM127 |
| Secreting paraganglioma | Extraprenal tumors of the sympathetic ganglia (para-aortic, vesicular, thoracic) primarily secreting norepinephrine ± dopamine; normetanephrine preferentially elevated; head and neck paragangliomas (carotid, jugular, vagal) — non-secreting in 95% of cases; SDHB associated with the highest risk of metastasis (30–40% of cases) |
| Neuroblastoma | Malignant tumor of the sympathetic nervous system in children (under 5 years of age in 90–95% of cases) — the third most common solid tumor in children; concomitant elevation of VMA and HVA in 90–95% of cases; VMA/HVA ratio > 1 — common; very high levels correlate with disease extent and prognosis; used for initial diagnosis and monitoring of response to treatment |
| Acute stress and intense pain | Physiological activation of the sympathoadrenal system — moderate elevations (usually < 2 times the normal limit) of free adrenaline and noradrenaline; fractionated metanephrines are little influenced by acute stress (continuous intracellular metabolism independent of secretion episodes); collection of 24-hour urine during a calm period is recommended |
| Chronic renal failure | Accumulation of catecholamines and their metabolites due to reduced renal clearance—interference with diagnostic thresholds; urinary catecholamine/creatinine ratios or plasma free metanephrines are preferable in cases of severe chronic kidney disease (eGFR < 30 mL/min). |
| Drug interactions | Antidepressants (tricyclics, SSRIs, SNRIs - venlafaxine particularly) → elevated urinary normetanephrines; MAO inhibitors (MAOIs) → catecholamine accumulation; labetalol (beta-blocker) → falsely positive catecholamines by fluorimetric method (analytical interference - absent with LC-MS/MS); buspirone, phenoxybenzamine, amphetamines, cocaine, levodopa (elevated dopamine and HVA); acetaminophen at high dose → false positive VMA by older colorimetric method |
| Food interference | Bananas, pineapple, nuts, chocolate, vanilla, coffee, tea (catecholamines and VMA); avoid 3 days before urine collection if using the colorimetric VMA method — less interference with LC-MS/MS; diet rich in tyrosine or phenylalanine → slight increase in precursors |
Dosage indications and collection conditions
- Main indications: suspicion of a pheochromocytoma or secreting paraganglioma (paroxysmal hypertension in crises, classic Ménard's triad: pulsating headaches + sweating + palpitations, resistant hypertension, incidentaloma discovered in the adrenal gland); at-risk family syndrome (MEN2, VHL, NF1, SDHx mutations) -> periodic screening; neuroblastoma in children (diagnosis and follow-up); assessment of secondary hypertension in young subjects (< 40 years old) or in cases of resistant hypertension to treatments
- 24-hour urine collection: collect in a container provided by the laboratory containing an acid preservative (6 N hydrochloric acid — maintains pH < 3 to stabilize catecholamines); measure total volume and note collection start and end times; refrigerate during collection; record urinary creatinine (collection validation — normal 24-hour creatinine: 8–18 mmol/24h in women, 10–22 mmol/24h in men); avoid intense exercise and major stress during collection; stop interfering medications 5 days prior if medically possible (in consultation with the prescribing physician).
- Free plasma metanephrines — first-line test: measured in a blood sample taken after 30 minutes of rest in the supine position in a quiet environment (to minimize sympathetic stress); sensitivity 97–99% for pheochromocytoma; specificity 85–89% (significant false-positive rate); slightly higher values when standing and under stress → strict collection under baseline conditions is essential; recommended as an initial test by the 2014 ETA and 2014 Endocrine Society guidelines
- Recommended diagnostic strategy: Start with free plasma metanephrines or fractionated urinary metanephrines (LC-MS/MS), depending on local availability; if the result is >3 times the upper limit of normal → very high probability of pheochromocytoma → direct imaging (MRI/CT scan of the adrenal glands); if result is 1 to 3 times the upper limit → gray area → repeat the test under optimal conditions (discontinue interfering medications, minimize stress) or perform a pharmacological suppression test (clonidine — not routinely performed in Quebec); if result is normal → pheochromocytoma highly unlikely (NPV > 99.1%)
Management based on results
| Result | Recommended course of action |
|---|---|
| Normal metanephrines, typical context for pheochromocytoma | Negative predictive value > 99% (1:3) — pheochromocytoma is highly unlikely; if there is strong clinical suspicion (typical Ménard’s triad + adrenal incidentaloma) → repeat the test or measure free plasma metanephrines; do not perform adrenal imaging as a first-line investigation if laboratory results are negative |
| Moderate elevation (1–3 x ULN) | Gray zone — exclude causes of false positives (medications, stress, CKD); repeat dosage under optimal conditions (stop interfering agents 5 days prior, calm collection, recumbent for plasma); endocrinology consultation recommended; clonidine suppression test may be considered in a specialized context |
| Clear elevation (> 3 x LN) | Highly suggestive of a secreting pheochromocytoma or paraganglioma — probability > 90% (%); Adrenal MRI or CT scan as first-line imaging (MRI preferred—better tissue characterization, no radiation exposure); if imaging is negative → investigate extra-adrenal sites (whole-body MRI + ¹²³I-MIBG scintigraphy or PET-DOTA-TATE if SDHB is mutated); urgent consultation with an endocrinologist; medical preparation for surgery (alpha-blocker phenoxybenzamine 10–14 days preoperatively + beta-blocker secondarily — never use a beta-blocker alone before the alpha-blocker) |
| VMA et HVA élevés chez l'enfant | Neuroblastome jusqu'à preuve du contraire — scanner abdominal et thoracique en urgence, scintigraphie MIBG, biopsie ostéomédullaire, consultations en onco-pédiatrie ; l'amplitude de l'élévation corrèle à l'extension tumorale et au pronostic ; suivi des marqueurs en cours de traitement pour évaluer la réponse |
| Mutation germinale SDHx / VHL / RET / NF1 identifiée | Dépistage biochimique (métanéphrines urinaires ou plasmatiques) annuel à biannuel selon le gène muté ; imagerie IRM corps entier tous les 1 à 3 ans ; suivi dans un centre expert en tumeurs neuroendocrines ; dépistage génétique des apparentés au premier degré |
Crise hypertensive paroxystique — urgence absolue
Dial 911 ou rendez-vous immédiatement à l'urgence en cas de crise hypertensive paroxystique (PA > 180/120 mmHg) accompagnée de céphalées intenses, de sueurs profuses, de palpitations, de douleur thoracique ou d'anxiété majeure — ce tableau peut correspondre à une décharge catécholaminergique massive d'un phéochromocytome non diagnostiqué. En urgence, la crise est traitée par phentolamine IV ou nicardipine IV (jamais de bêta-bloquant seul en première intention sans alpha-bloquant préalable — risque de vasoconstriction paradoxale majeure). Un diagnostic de phéochromocytome non traité expose à un risque de mort subite par arythmie ou accident vasculaire cérébral hémorragique lors de toute procédure invasive (chirurgie, accouchement, coloscopie, intubation).
Consult at Clinique Omicron
Les médecins de Clinique Omicron prescrivent le dosage des catécholamines et métanéphrines urinaires, informent sur les conditions de recueil optimal, interprètent les résultats en contexte clinique et orientent vers l'endocrinologue ou le spécialiste en médecine nucléaire pour la prise en charge diagnostique et thérapeutique des phéochromocytomes, paragangliomes et neuroblastomes. Des consultations sont disponibles dans nos points de service au Québec ainsi qu'en télémédecine. Pour prendre rendez-vous, visitez cliniqueomicron.ca.
Le contenu de cette page est fourni à titre informatif uniquement et ne remplace pas l'avis d'un professionnel de santé qualifié. Les valeurs de référence des catécholamines et de leurs métabolites varient selon les laboratoires et les méthodes analytiques — toujours se référer aux valeurs de référence du laboratoire ayant effectué l'analyse.
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