High Metanephrines: What Does the Result Mean and What Happens Next?

High metanephrines mean that breakdown products of adrenaline and noradrenaline were above the laboratory's reference range in your blood or urine. The test is used to screen for phaeochromocytoma and paraganglioma, which are rare tumours. Many raised results, especially mild ones, turn out to be false positives caused by medicines, stress or sampling conditions.

This guide is for adults who already have a result and want to understand it. It cannot tell you whether your result is significant. Only the clinician who ordered the test, with your full history, can interpret it.

A test result on its own is rarely an emergency, but some symptoms are. Do not wait for a repeat test or a routine appointment if you have any of the following. Call local emergency services.

• Chest pain that does not go away, or pain spreading to the arm, neck, jaw or back, especially with sweating, sickness or breathlessness.
• Signs of a possible stroke: one side of the face drooping, weakness in one arm, or slurred or confused speech, even if they pass.
• Repeated sudden attacks of pounding heartbeat, severe headache and heavy sweating that are getting more frequent or severe: contact your clinician the same day.

There are two main screening tests. Plasma free metanephrines is a blood test. Urinary fractionated metanephrines usually uses a 24-hour urine collection. The Endocrine Society guideline accepts either as a first test.

Each has trade-offs. A Cleveland Clinic Journal of Medicine review reports that the plasma test is more sensitive, so a normal plasma result is more reassuring, but that its specificity is lower, so it produces more false positives. Plasma testing may be preferred when kidney function is reduced. A urine collection can be more practical when the blood sample cannot be taken under the ideal conditions.

Your report may list normetanephrine and metanephrine separately. Note which one is raised and by how much, because clinicians look at the pattern, not just a single flag.

If you are asked to do a 24-hour urine collection, MedlinePlus describes the usual method: pass and discard the first urine, note the time, collect all urine for the next 24 hours and keep the container cold. A missed sample can make the result harder to interpret, so tell the laboratory if this happens.

A false positive is a raised result in someone who does not have a tumour. Sources describe several common causes.

• Posture during sampling: the guideline suggests taking blood while lying down, with reference ranges set in the same position. Seated samples raise the chance of a false positive. Some services place a small cannula and ask you to rest lying down beforehand.
• Medicines: some medicines raise metanephrine levels or interfere with the laboratory method. Examples named in the sources include tricyclic antidepressants, paracetamol (acetaminophen), methyldopa and some other blood pressure medicines.
• Stress and illness: physical stress such as a serious illness can raise results. Testing is usually repeated once a person is well again.
• Caffeine, alcohol, smoking and hard exercise shortly before the test can also affect related results.

Do not stop any prescribed medicine on your own. Stopping some medicines suddenly can be harmful. Bring a full list of everything you take, including non-prescription products and supplements, and ask whether any of them could affect the result.

If a change is needed, the clinician will decide whether it is safe, how and when to do it, and when to retest. Ask the testing service for its own preparation instructions about food, drink, smoking and rest.

Size matters. The Cleveland Clinic Journal of Medicine review notes that a rise of three to four times the upper reference limit is unlikely to be a false positive, while smaller rises are often called equivocal. Reference ranges and methods differ between laboratories, so use the range printed on your own report.

For a mild or borderline result, repeating the test under better conditions is common. That may mean a lying-down blood sample, a urine collection, or retesting after a medicine review. In some cases a specialist may use a further test, such as a clonidine suppression test. Imaging such as CT or MRI is usually used to find a tumour after the blood or urine results point towards one, not as a first step.

If a tumour is found, genetic testing may be offered. The NHS notes that up to one in three cases are linked to inherited conditions.

Phaeochromocytoma is a rare tumour of the adrenal medulla. Paraganglioma is a related tumour outside the adrenal glands. Possible symptoms include episodes of headache, sweating and a pounding heartbeat, and high blood pressure that may be hard to control. Some people have no symptoms, and the tumour is found on a scan done for another reason.

If you had metanephrines checked because a scan showed an adrenal nodule, see our guide on why adrenal nodules need hormone assessment. If the test was prompted by blood pressure readings that vary between home and clinic, our guide on that topic explains what to record. When a tumour is confirmed, the NHS describes surgery as the main treatment, and it is usually successful.

Take your report to the appointment and write down the answers.

• Which result is raised, normetanephrine or metanephrine, and how many times above the upper limit is it?
• Was my blood taken lying down or sitting, and does that change how you read it?
• Could any of my medicines, a recent illness or stress explain the result?
• Do I need a repeat test, and if so which type, how should I prepare, and when?
• What result would lead you to arrange a scan or a referral to an endocrinologist?
• Who will contact me with the result, and by when?

On SameCase, patients and verified doctors share de-identified cases. Reading how other people's raised metanephrine results were followed up, for example which ones were repeated lying down or after a medicine review, can help you think of questions to bring to your own clinician.

Other people's cases cannot tell you what your result means or what you should do. We do not diagnose, and decisions about your tests and treatment stay with the clinicians who know your history.