Plasma fractionated metanephrines refer to a specialized blood test that measures metanephrine and normetanephrine levels in the bloodstream. These substances are breakdown products of hormones. The test is primarily used to identify rare conditions involving the overproduction of these hormones.
Understanding Metanephrines
Metanephrines are metabolites, or breakdown products, of catecholamines, a group of hormones including epinephrine (adrenaline) and norepinephrine (noradrenaline). These catecholamines are primarily synthesized and stored in the chromaffin cells of the adrenal medulla, located atop the kidneys.
The body releases catecholamines in response to physical or emotional stress, preparing for a “fight or flight” response. They influence heart rate, blood pressure, and metabolism. Once released, catecholamines are broken down into metanephrines and normetanephrines.
These metanephrines are eventually excreted from the body. Measuring their levels in the blood, specifically the “fractionated” plasma test, allows for the separate quantification of metanephrine and normetanephrine. This distinction helps identify which specific catecholamine might be overproduced, providing more precise diagnostic information.
Why the Test is Performed
The plasma fractionated metanephrines test is primarily performed to screen for and diagnose rare neuroendocrine tumors: pheochromocytomas and paragangliomas. Pheochromocytomas originate in the adrenal glands, while paragangliomas develop outside the adrenal glands. Both tumor types can produce excessive catecholamines, leading to various symptoms.
Individuals experiencing symptoms suggestive of catecholamine overproduction are often recommended for this test. Common symptoms include persistent or episodic high blood pressure, rapid heart rate (tachycardia), palpitations, and severe headaches.
Patients might also report excessive sweating, tremors, anxiety or panic attacks, abdominal pain, nausea, and vomiting. The test is useful because these tumors continuously or intermittently release catecholamines, leading to elevated metanephrine levels even when the patient is not actively experiencing symptoms.
Preparing for the Test and What to Expect
Preparing for a plasma fractionated metanephrines test is important to ensure accurate results, as various factors can influence catecholamine and metanephrine levels. Patients are typically advised to avoid certain foods, beverages, and medications for a specified period before the blood draw. This usually includes abstaining from caffeine, alcohol, and nicotine for at least 24 hours prior to the test.
Certain foods and some over-the-counter and prescription medications can affect the results. Patients should discuss all medications with their healthcare provider beforehand, as some may need to be temporarily discontinued under medical supervision.
Reducing stress and physical activity before the test is also beneficial, as these can temporarily elevate catecholamine levels. Patients are often instructed to rest quietly for 15-30 minutes before the blood sample is taken. The procedure involves a standard blood draw from a vein, typically in the arm.
Interpreting Your Results
Interpreting plasma fractionated metanephrines test results requires careful consideration by a healthcare professional. Normal levels of metanephrine and normetanephrine generally indicate no significant overproduction of catecholamines from a tumor. These reference ranges can vary slightly between laboratories, but typically, metanephrine levels are below approximately 90 pg/mL and normetanephrine levels are below about 180 pg/mL.
Elevated levels of either metanephrine or normetanephrine suggest the possibility of a pheochromocytoma or paraganglioma. The degree of elevation can sometimes correlate with the size or activity of the tumor, but even slight increases warrant further investigation. Elevated results do not provide a definitive diagnosis on their own.
Other factors, such as stress, certain medications, or even vigorous exercise before the test, can lead to false positive results. If initial results are elevated, a healthcare provider will likely recommend confirmatory tests, such as a 24-hour urine collection for metanephrines, or imaging studies like MRI or CT scans. Discussing all results and next steps with a qualified medical professional is paramount for accurate diagnosis and appropriate management.