Metanephrine- Fractionated Plasma

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Fasting Required

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Catecholamine metabolites.

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Metanephrine - Fractionated Plasma Test Guide

Why is it done?
- Measures plasma levels of free metanephrines (epinephrine and norepinephrine metabolites) to detect catecholamine-secreting tumors
- Primary indication: Screening for pheochromocytoma and paraganglioma in patients with suspected catecholamine excess
- Evaluates patients presenting with hypertension, palpitations, excessive sweating, headaches, or anxiety attacks
- Used in genetic syndromes associated with pheochromocytoma (MEN2A, MEN2B, NF1, VHL)
- Monitoring patients with known pheochromocytoma or paraganglioma after surgical treatment or during medical management
- Typically performed in the supine position after 30 minutes of rest to obtain baseline values
Normal Range
- Plasma Free Metanephrines (Reference Range):
- Normetanephrine: 0.4-0.9 nmol/L (or <0.9 nmol/L) or <0.61-0.89 nmol/L depending on laboratory
- Metanephrine: 0.1-0.3 nmol/L (or <0.3 nmol/L) or <0.10-0.31 nmol/L depending on laboratory
- Total metanephrines: <1.2 nmol/L
- Units: nmol/L (nanomoles per liter) or pg/mL (picograms per milliliter)
- Interpretation:
- Normal: Values within reference range suggest absence of pheochromocytoma (>99% sensitive when normal)
- Elevated: Values above upper reference limit suggest possible catecholamine-secreting tumor; typically >1.4x upper reference limit is considered positive
- Borderline: Results between upper limit of normal and 1.4x upper limit warrant repeat testing or further investigation
- Reference ranges vary by laboratory method and patient position; always refer to specific laboratory reference values
Interpretation
- Elevated Metanephrines:
- Strongly suggestive of pheochromocytoma or paraganglioma, particularly if markedly elevated (>2x upper limit of normal)
- Elevated normetanephrine suggests tumor secreting norepinephrine
- Elevated metanephrine alone may indicate tumor secreting primarily epinephrine (adrenal origin)
- Normal Results:
- Effectively rules out pheochromocytoma with >99% sensitivity when properly collected and within normal range
- Symptoms suggestive of pheochromocytoma with normal metanephrines suggest alternative diagnoses
- Factors Affecting Results:
- Patient position and stress level: Standing vs supine position affects values significantly
- Medications: Decongestants, stimulants, tricyclic antidepressants, sympathomimetic agents can elevate results
- Recent exercise, caffeine intake, nicotine, and emotional stress can cause false elevations
- Acute illness, sleep apnea, and certain medical conditions may elevate metanephrines
- Improper blood collection technique or sample handling can invalidate results
- Clinical Significance:
- This test is the gold standard initial screening for catecholamine-secreting tumors due to superior sensitivity
- More sensitive than 24-hour urine metanephrines for detecting pheochromocytoma
- Helps differentiate true pheochromocytoma from pseudo-pheochromocytoma or essential hypertension
Associated Organs
- Primary Organs/Systems:
- Adrenal medulla: Primary site of pheochromocytoma (80-90% of cases)
- Sympathetic nervous system: Paraganglioma can occur along sympathetic chain
- Cardiovascular system: Affected by excessive catecholamine secretion
- Medical Conditions Associated with Abnormal Results:
- Pheochromocytoma: Catecholamine-secreting tumor of adrenal medulla (90-95% malignant potential of 10%)
- Paraganglioma: Extra-adrenal catecholamine-secreting tumor; higher malignancy rate (30-40%) than adrenal pheochromocytoma
- Multiple Endocrine Neoplasia Type 2 (MEN2A and MEN2B): Genetic predisposition to pheochromocytoma
- Neurofibromatosis Type 1 (NF1): Associated with increased pheochromocytoma risk
- Von Hippel-Lindau Disease (VHL): High risk for pheochromocytoma development
- Potential Complications of Untreated Abnormal Results:
- Hypertensive crisis: Acute, severe elevation in blood pressure
- Myocardial infarction: Due to catecholamine-induced increased cardiac demand
- Arrhythmias: Life-threatening cardiac dysrhythmias from excessive catecholamines
- Pulmonary edema: Secondary to hypertensive crisis
- Stroke: Hypertension-related cerebrovascular event
- Tumor metastasis: Malignant paragangliomas can spread systemically if not identified and treated
Follow-up Tests
- Confirmatory Tests if Results Elevated:
- 24-hour Urine Free Metanephrines and Catecholamines: Confirmation of plasma results
- Clonidine Suppression Test: To distinguish true pheochromocytoma from secondary causes of elevated catecholamines
- Imaging Studies:
- CT Abdomen and Pelvis: Standard imaging to locate adrenal masses
- MRI Abdomen: Alternative imaging, better for characterizing adrenal lesions
- I-123 MIBG Scan: Functional imaging for pheochromocytoma and paraganglioma detection
- PET-CT with 18F-FDG or 68Ga-DOTATATE: Enhanced detection for malignant paragangliomas and metastases
- Complementary Laboratory Tests:
- Plasma Catecholamines (Epinephrine, Norepinephrine): Direct measurement of catecholamine levels
- Chromogranin A: Tumor marker, elevated in pheochromocytoma and paraganglioma
- Blood Pressure Monitoring: 24-hour ambulatory BP monitoring or home BP log to assess hypertension
- Electrocardiogram (ECG): To assess for catecholamine-induced cardiac effects
- Genetic Testing:
- SDHA, SDHB, SDHD, SDHAF2 gene testing: For familial paraganglioma syndrome
- RET proto-oncogene testing: For MEN2 syndromes
- NF1 gene testing: For neurofibromatosis type 1
- Monitoring Frequency:
- Post-surgical: Metanephrines typically checked at 1-2 weeks post-op, then periodically (every 3-6 months initially, then annually)
- Genetic syndrome carriers: Annual or biennial screening recommended
- Known malignancy: More frequent monitoring (quarterly to semi-annually) depending on treatment plan
Fasting Required?
- Fasting Status: Fasting is NOT required for this test
- Patient Preparation Requirements:
- Rest in supine position (lying down) for 30 minutes before blood draw to obtain standardized baseline
- Maintain calm environment: Minimize stress and anxiety which can artificially elevate catecholamine levels
- Avoid caffeine for at least 12 hours before testing
- Avoid nicotine/tobacco for at least 1 hour before testing
- No vigorous exercise for 24 hours prior to test
- Medications to Avoid or Discuss:
- Decongestants (pseudoephedrine, phenylephrine): Can cause false elevation in metanephrines
- Sympathomimetic agents: Amphetamines, methylphenidate, ephedrine should be avoided
- Tricyclic antidepressants (amitriptyline, imipramine): May elevate results; discuss with ordering physician
- Antihistamines (first generation): Can cause elevation; avoid 48 hours prior if possible
- Cold and cough medications: Contain sympathomimetic agents; avoid 24 hours prior
- Appetite suppressants: Can elevate metanephrines; coordinate with ordering physician
- Note: Do NOT discontinue essential medications (antihypertensives) without physician approval; inform lab of all current medications
- Dietary Considerations:
- Avoid tyramine-rich foods 24 hours prior: Aged cheeses, cured meats, fermented foods, soy sauce, some Asian dishes
- Light meals acceptable; normal eating pattern is encouraged unless otherwise instructed
- Collection Procedure Notes:
- Blood collected via peripheral vein puncture into tubes with specific anticoagulant (usually EDTA or heparin)
- Sample must be placed on ice immediately after collection and transported rapidly to lab
- Plasma must be separated within 15 minutes of collection to prevent in vitro catecholamine release
- Proper handling is critical to avoid falsely elevated results

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