Metanephrines, Fractionated, Plasma Free
Code:9039|CPT:83835|LOINC:2669-0, 38494-1
| Includes | Normetanephrine, plasma free Metanephrine, plasma free |
|---|
Analysis details
Methodology
- Liquid chromatography–tandem mass spectrometry (LC-MS/MS)
Expected Turnaround Time
1–2 days
Special Instructions
- If collection after full supine rest is not feasible, use a 24-hour urine metanephrines study instead.
- Infants younger than 1 year: withhold feeds for 30–40 minutes before the draw.
- Children 1–5 years: fast for 2–3 hours prior to collection.
- Adolescents and adults: fast for 12 hours; water is allowed.
- Avoid avocado, bananas, eggplant, pineapple, plums, tomatoes, and walnuts for 72 hours before collection.
- With clinician approval, stop sympathomimetic agents 14 days before the test.
- With clinician approval, avoid all nonessential medications for 24 hours before collection.
- Do not smoke during the 2 hours before collection.
How to use
Metanephrines, Fractionated, Plasma Free (free metanephrine and free normetanephrine) is used to assess for catecholamine-secreting tumors, including adrenal pheochromocytoma and extra-adrenal sympathetic or parasympathetic paragangliomas. The test also assists in gauging response to treatment and in surveillance for recurrence, and it can be selected when urine metanephrines are not feasible or yield equivocal results.
Limitations
Metanephrines are terminal O-methylated metabolites in catecholamine biotransformation: norepinephrine forms normetanephrine and epinephrine forms metanephrine. Quantifying free (unconjugated) metanephrines in plasma offers greater diagnostic sensitivity than measuring catecholamines directly, because circulating catecholamines fluctuate rapidly and are stress labile. Abnormal results require correlation with clinical probability and may prompt confirmatory testing or imaging, guided by the magnitude and pattern of elevation. Inadequate collection conditions and physiologic stress can produce false-positive increases and should be considered during interpretation.
| Unit | pg/mL | ||||
|---|---|---|---|---|---|
| Reference interval |
| ||||
| Indications | Evaluation of episodic or sustained hypertension accompanied by tachycardia, flushing, or excessive sweating, Hypertension that remains uncontrolled despite appropriate therapy, Incidentally detected adrenal mass or other neuroendocrine incidentaloma on imaging, First-degree family history of pheochromocytoma or paraganglioma |
Possible Causes of Abnormal Results
Increased levels
- alpha blockers
- caffeine
- carcinoid tumor
- cigarette smoking
- ganglioneuroblastoma
- ganglioneuroma
- hepatitis
- hypoglycemia (insulin-induced)
- monoamine oxidase inhibitors
- neuroblastoma
- neuroendocrine tumor
- paraganglioma
- pheochromocytoma
- renal impairment
- serotonin and norepinephrine reuptake inhibitors
- strenuous exercise
- sympathomimetics
Decreased levels
- aromatic l-amino acid decarboxylase deficiency
- biopterin deficiency
- dopamine beta-hydroxylase deficiency
- iron deficiency
- sepiapterin reductase deficiency
- tyrosine hydroxylase deficiency
- vitamin b3 deficiency
Specimen Requirements
| Specimen | Plasma |
|---|---|
| Container | Light Blue Top (3.2% Sodium Citrate) |
| Volume | 1.2 mL (min 0.7 mL) |
| Storage Instructions | Refrigerated, Frozen |