Urinary Metanepherine (24 Hours)

Kidney

Report in 144Hrs

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No Fasting Required

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Catecholamine metabolite.

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Urinary Metanepherine (24 Hours) - Comprehensive Medical Test Guide

Why is it done?
- Test Description: This test measures metanephrines (metabolites of catecholamines) in urine collected over 24 hours to detect abnormal levels of these hormones, which may indicate pheochromocytoma or paraganglioma.
- Primary Indications: Suspected pheochromocytoma with symptoms including severe hypertension, sudden severe headaches, profuse sweating, palpitations, and tremor; screening for paraganglioma; evaluation of familial syndromes (MEN 2, NF1, SDH mutations); assessment of drug-resistant hypertension; investigation of episodic symptoms suggestive of catecholamine excess.
- Timing and Circumstances: Performed when clinical features suggest catecholamine-secreting tumors; recommended before imaging studies; used as initial screening test given high sensitivity; may be repeated during acute episodes or hypertensive crises; part of diagnostic workup before surgery.
Normal Range
- Reference Values: Total metanephrines: <275 µg/24 hours (or <1.5 µmol/24 hours); Metanephrine (from epinephrine): <100 µg/24 hours; Normetanephrine (from norepinephrine): <175 µg/24 hours. Reference ranges may vary slightly between laboratories depending on methodology used.
- Interpretation Guidelines: Negative result (values within normal range): Significantly reduces likelihood of pheochromocytoma; indicates adequate catecholamine control in patients on treatment; suggests symptoms are not due to catecholamine excess.
- Positive Result: Values >4 times upper limit of normal are highly specific for pheochromocytoma; values 1-4 times upper limit may warrant repeat testing; borderline elevated values (1-2 times normal) require clinical correlation and possible confirmatory testing.
- Units of Measurement: Micrograms per 24 hours (µg/24h) or micromoles per 24 hours (µmol/24h); laboratory reports should clearly specify which components are measured (total metanephrines, metanephrine, normetanephrine, or combined).
- Normal vs Abnormal Significance: Normal values have >90% sensitivity for excluding pheochromocytoma in patients with classic presentation; abnormal values have 89-99% specificity for diagnosis; persistently normal results on repeat testing have exceptional negative predictive value.
Interpretation
- Markedly Elevated Results (>4x upper normal limit): Highly suggestive of pheochromocytoma or paraganglioma; requires immediate imaging (CT or MRI of abdomen/pelvis) and specialist referral; indicates need for alpha-blockade therapy before surgical intervention; patient should be monitored closely for hypertensive crises.
- Mildly to Moderately Elevated (1-4x upper normal limit): Warrants repeat 24-hour urine collection to exclude laboratory error or false positive; repeat testing on separate occasion shows 95% specificity; may require confirmatory plasma free metanephrines testing; clinical symptoms should be carefully reviewed.
- Normal Results with High Clinical Suspicion: Pheochromocytoma unlikely but not completely excluded; repeat testing recommended if symptoms persist; consider plasma free metanephrines as alternative confirmatory test; evaluate for other causes of hypertension and symptoms.
- Factors Affecting Results: Certain medications (decongestants, methylphenidate, tricyclic antidepressants, sympathomimetics) may increase levels; caffeine, stress, exercise, and smoking can elevate values; incomplete or improperly stored urine collections cause false negatives; medications should be discontinued 1-2 weeks before testing when clinically possible.
- Clinical Significance of Result Patterns: Predominantly elevated normetanephrine suggests noradrenaline-secreting tumor (more common); predominantly elevated metanephrine suggests adrenal medullary pheochromocytoma; combined elevation increases diagnostic likelihood; pattern helps predict tumor location and type.
Associated Organs
- Primary Organ Systems: Adrenal medulla (primary source of metanephrines); sympathetic nervous system (extra-adrenal sites); kidneys and urinary system (route of excretion); cardiovascular system (target of catecholamine effects).
- Diseases Diagnosed or Monitored: Pheochromocytoma (adrenal catecholamine-secreting tumor); paraganglioma (extra-adrenal pheochromocytoma); multiple endocrine neoplasia type 2 (MEN 2A and 2B); neurofibromatosis type 1 (NF1); familial paraganglioma syndromes; hereditary paraganglioma-pheochromocytoma syndrome (SDH mutations).
- Complications Associated with Abnormal Results: Hypertensive crisis and acute myocardial infarction; stroke and cerebrovascular accident; pulmonary edema; arrhythmias and sudden cardiac death; left ventricular hypertrophy; acute kidney injury; retinopathy; if untreated before surgery, severe intraoperative hypertension and postoperative hypotension may occur.
- Pathophysiological Effects: Excessive catecholamine release causes sustained or paroxysmal hypertension, tachycardia, and metabolic effects; chronic exposure increases cardiovascular morbidity; episodic release may cause dramatic but transient symptoms; tumor growth can compress adjacent organs and cause local effects.
Follow-up Tests
- Confirmatory Tests (if elevated results): Plasma free metanephrines (considered gold standard confirmatory test); repeat 24-hour urine metanephrines on separate occasion; supine and standing plasma catecholamine levels; clonidine suppression test if plasma catecholamines borderline.
- Imaging Studies: CT or MRI of abdomen and pelvis (initial localization); MIBG scan (meta-iodobenzylguanidine scintigraphy) for detecting extra-adrenal sites; PET/CT with F-18 fluorodopamine for paraganglioma localization; consider chest imaging for intrathoracic paragangliomas.
- Genetic Testing: RET proto-oncogene mutation testing (MEN 2); NF1 gene testing (neurofibromatosis); SDH gene panel testing (SDHA, SDHB, SDHC, SDHD, SDHAF2); VHL testing (von Hippel-Lindau syndrome); TMEM127 and MAX testing.
- Pre-operative Assessment: Electrocardiography (ECG) to assess cardiac status; echocardiography if cardiomyopathy suspected; blood glucose and lipid panels; urinalysis; baseline blood pressure monitoring.
- Monitoring Frequency: Post-operative: repeat urinary metanephrines 1-2 weeks after surgery to confirm tumor removal; if persistent elevation, suggests incomplete resection or metastatic disease; long-term follow-up recommended for genetic predisposition syndromes; annually in asymptomatic patients with family history.
- Related Complementary Tests: 24-hour urine catecholamines; urine vanillylmandelic acid (VMA); plasma chromogranin A; urinary fractionated metanephrines; blood glucose; aldosterone and renin activity (if hypertension requires explanation); thyroid function tests.
Fasting Required?
- Fasting Status: No fasting is required for this test. The 24-hour urine collection test is not affected by food intake, and patients may eat and drink normally during the collection period.
- Medications to Avoid: Decongestants containing pseudoephedrine or phenylephrine; over-the-counter cold medications; methylphenidate and other ADHD medications; tricyclic antidepressants (amitriptyline, imipramine); sympathomimetic amines; nasal decongestants; appetite suppressants. Discontinue these medications 1-2 weeks before testing if clinically possible and approved by physician. Discuss all medications with healthcare provider before testing.
- Lifestyle Modifications: Avoid excessive stress and physical exertion during collection period; limit caffeinated beverages (coffee, tea, energy drinks, cola) 24 hours before and during collection; avoid smoking 24 hours before and during collection; avoid vigorous exercise during collection period; maintain normal daily routine for accurate results.
- Patient Preparation Requirements: Obtain 24-hour urine collection container (usually 2-liter jug with preservative) from laboratory; begin collection first thing in morning by discarding first void; collect all urine for next 24 hours including first void next morning; keep container in cool environment or refrigerated during collection; label container with name, date, and time of start and completion; return container promptly to laboratory for processing.
- Important Preparation Notes: Specimen validity depends on complete 24-hour collection; improper storage or incomplete collection leads to false negative results; use container provided by laboratory as it contains proper preservative; if any urine is accidentally discarded during collection period, collection must be restarted; inform laboratory of any intercurrent illness or stressful events during collection; some laboratories recommend supine rest 30 minutes before start of collection for standardization.

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