At a glance

Also known as

Plasma metanephrine

Why get tested?

To help diagnose or rule out a phaeochromocytoma

When to get tested?

If you have symptoms of persistent or episodic high blood pressure such as severe headaches, rapid heart rate and sweating

Sample required?

A blood sample drawn from a vein in your arm

Test preparation needed?

Pre-sample preparation is important for accurate results. Talk to your doctor about all the medications you are taking since several different drugs may interfere with the test.

What is being tested?

The plasma free metanephrines test measures the amount of metanephrine and normetanephrine in the blood. These substances are metabolites of adrenaline and noradrenaline. Adrenaline and noradrenaline are catecholamine hormones that help regulate the flow and pressure of blood throughout the body and play important roles in the body’s response to stress. They are produced in the medulla (interior) of the adrenal glands. Each person has two adrenal glands and they are small, triangular organs located on top of the kidneys. The catecholamines that the adrenal glands create, and their metabolites (metanephrine and normetanephrine), are normally found in small fluctuating quantities in both the blood and urine.

A rare tumour called a phaeochromocytoma can produce large amounts of catecholamines, resulting in significantly increased concentrations of metanephrine and normetanephrine in both the blood and urine. About 90% of phaeochromocytomas form in the adrenal glands and, while a few are cancerous, most are benign – they do not spread beyond their original location - although most do continue to grow.

The catecholamines that phaeochromocytomas produce can cause persistent hypertension (high blood pressure) and/or paroxysms (bouts) of severe high blood pressure. This can cause symptoms such as headaches, palpitations, sweating, nausea, anxiety, and tingling in the extremities. Left untreated, the symptoms may worsen as the phaeochromocytoma grows and, over a period of time, the high blood pressure that the tumour causes may damage body organs such as the kidneys and heart and raise the risk of an affected patient having a stroke or heart attack.

Plasma free metanephrines and urine catecholamines can be used to detect the presence of phaeochromocytomas. It is important to diagnose and treat these rare tumours because they cause a potentially curable form of high blood pressure. In most cases, the tumours can be surgically removed and/or treated to significantly reduce the amount of catecholamines being produced and to reduce or eliminate their associated symptoms and complications.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in your arm. There is some variation between laboratories in the specifics of how the sample is collected. At the collection site, you may be asked to lie down and rest quietly for 15 – 30 minutes prior to sample collection, and your blood may be collected while you are lying down. In other circumstances, you may just be seated upright with little or no rest time before the sample collection.

Is any test preparation needed to ensure the quality of the sample?

Pre-sample preparation is important for accurate results. Talk to your doctor about all the medications you are taking since several different drugs may interfere with the test.

The Test

How is it used?

Plasma free metanephrines is a test used to help diagnose or rule out the presence of a phaeochromocytoma. Studies have shown that plasma testing is more sensitive than the more traditional 24-hour urine catecholamines testing. However, this sensitivity brings with it a certain number of false positive results, especially when the test is ordered on patients who do not have a high likelihood of having a phaeochromocytoma. For this reason, plasma free metanephrines is not recommended as a screen for the general public. Its primary use is to screen symptomatic patients to detect and to help rule out the likely presence of a phaeochromocytoma.

Since the tests results may be affected by stress, caffeine, alcohol, and certain drugs, a doctor may investigate a positive result by evaluating a patient’s stresses and intake, alter or minimise these influences, and then repeat the test to confirm the original findings.

Occasionally, the test may be ordered on an asymptomatic person if an adrenal tumour is detected during a scan that is done for another purpose or if the patient has a strong personal or family history of phaeochromocytomas (as they may recur, and there is a genetic link in some cases).

When is it requested?

The plasma free metanephrines test is primarily ordered when a doctor either suspects that a patient has a phaeochromocytoma or wants to rule out the possibility. The doctor may order it when a patient has persistent or recurring symptoms suggesting marked high blood pressure, such as headaches, sweating, flushing, and rapid heart rate. It may also be ordered when a patient has high blood pressure that is not responding to treatment (patients with a phaeochromocytoma are frequently resistant to conventional therapies).

Occasionally, the test may be ordered when an adrenal tumour is detected incidentally or when a patient has a family history of phaeochromocytomas. It may also be used as a monitoring tool when a patient has been treated for a previous phaeochromocytoma.

What does the test result mean?

Since the plasma free metanephrines test is very sensitive and phaeochromocytomas are rare, a doctor may see more false positives with this test than true positives. The negative predictive value of the test, however, is very good. This means that if the concentrations of the free metanephrines are normal in the blood, then it is very unlikely that a patient has a phaeochromocytoma.

If a symptomatic patient has large amounts of free metanephrines in their blood, then it is likely that they have a phaeochromocytoma. The doctor may order imaging tests (such as an MRI scan) to help find the tumour(s). If an asymptomatic patient with a tumour that has been discovered during a scan for another reason has significantly elevated free metanephrines, then it is likely that the tumour discovered is a phaeochromocytoma.

If a symptomatic or asymptomatic patient has only moderately elevated free metanephrines, then the doctor may re-evaluate the patient’s medications, diet, and stress level to look for interfering substances. The doctor may then re-test the patient, perhaps along with 24-hour urine catecholamine testing, to determine whether the free metanephrines are still elevated. If they are, then the doctor may order imaging scans; if they are not, then it is unlikely that the patient has a phaeochromocytoma.

If levels are elevated in a patient who has had a previous phaeochromocytoma, then it is likely that either treatment was not fully effective or that the tumour is recurring.

About Reference or “Normal” Ranges

Is there anything else I should know?

While the plasma free metanephrines test can help detect and diagnose phaeochromocytomas, it cannot tell the doctor where the tumour is (although the majority are found in the adrenal gland and most of the rest are found within the abdominal cavity). It also cannot tell the doctor whether or not the tumour is benign (although most are).

Common Questions

Can I have more than one phaeochromocytoma at once?

Yes, especially when there is a strong family history of phaeochromocytomas. A patient may have a tumour in each adrenal gland.

Does the amount of plasma free metanephrines detected correspond to the size of the tumour?

No, it has more to do with the characteristics of the tumour. Even a very small tumour can produce large amounts of catecholamines.

Is it really necessary to follow the dietary restrictions and lie down before testing?

There is some disagreement over the specifics of how the sample should be collected. However, it is known that the level of catecholamines (and their metabolites) in the blood is affected by diet and stress levels. For test accuracy, interfering substances need to be avoided and the patient’s physical and emotional stress levels should be as low as possible.

Last Review Date: February 13, 2015