Also known as: Free metanephrines
Name: Plasma free metanephrines (normetanephrine and metanephrine)
Related tests: Plasma and urine catecholamines, Urine metanephrines
When to get tested?
When there are episodes of high blood pressure, sporadic or continuous, with symptoms such as headache, rapid heartbeat and excessive sweating
What sample is the test carried out on?
A blood sample from a vein
Is any preparation needed for the test?
Preparation is very important for the test result to be accurate. Treatment with adrenaline and related medicines must be stopped a week before the test, and paracetamol (acetaminophen) must not be taken in the 48 hours before the test. In the four hours before the test it is very important not to smoke or take caffeine (including foods containing caffeine, such as chocolate), theine or alcohol. You should in any case talk to your doctor about other medicines that may affect the test result
What is being tested?
The test measures the concentration of the free portion of metanephrines in the plasma, which is proportional to the concentration of metanephrine and normetanephrine in the blood. These substances are metabolites of adrenaline and noradrenaline, which are catecholamines involved in regulating blood pressure, circulation and the response to stress. They are produced by the medulla of the adrenal glands. Catecholamines are present in small concentrations in both blood and urine.
A rare form of tumour called phaeochromocytoma increases the production of metanephrine and normetanephrine in the blood and urine. In 90% of cases this disease originates in the adrenal glands; most forms are benign, and the mass continues to grow without spreading to other sites. The catecholamines produced by a phaeochromocytoma can cause high blood pressure, which causes symptoms such as headache, palpitations, excessive sweating, nausea, anxiety and tingling. If left untreated, the tumour may grow and the symptoms get worse; sometimes the high blood pressure can damage the kidneys and heart and cause strokes or heart attacks.
Some tests, such as free metanephrines, can help diagnose phaeochromocytoma, whose associated symptoms can be treated and which can sometimes be removed surgically.
How are the samples collected for testing?
The blood sample is taken from a vein in the arm. Opinions differ on how the sample should be taken. Some have the patient rest for 15-30 minutes before the sample, while others do not have them rest at all; some take the sample with the patient lying down, others with the patient seated.
Is any preparation needed for the result to be accurate?
Preparation is very important for the accuracy of the result. Do not take adrenaline or related medicines for a week before the test, and avoid paracetamol (acetaminophen) for 48 hours before. Do not take caffeine (including foods that contain it, such as chocolate), theine or tobacco in the four hours before the test. You should in any case consult your doctor about the medicines you are taking and before stopping any treatment.
How is it used?
When is the test requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
Plasma free metanephrine testing is a relatively new test, and there are not yet adequate guidelines for interpreting it. Numerous studies have shown that this test is more sensitive than urine metanephrines and catecholamines. On the other hand, it is associated with a number of false positives, especially when used to detect phaeochromocytoma. For this reason the test is not recommended as a routine test; it is used only in patients with symptoms when the urine test does not give a clear result. Since the test result is affected by stress and diet, if the result is positive the doctor often has the patient repeat the test (after reducing exposure to these factors) to confirm the result.
Occasionally the test is requested even without symptoms, if an adrenal tumour is found on an ultrasound scan or if there are cases of phaeochromocytoma in the patient’s family.
When is the test requested?
When phaeochromocytoma is suspected. The symptoms associated with this disease are high blood pressure, headache, excessive sweating, tingling and a rapid heartbeat. It is also often requested in patients who do not respond to conventional treatment for high blood pressure (as happens with phaeochromocytoma).
Occasionally the test is requested even without symptoms, if an adrenal tumour is found on an ultrasound scan or if there are cases of phaeochromocytoma in the patient’s family.
The test is also used to monitor treatment.
What does the test result mean?
Is there anything else I should know?
Most phaeochromocytomas are located in the adrenal glands. However, plasma free metanephrines do not tell the doctor where the tumour is, or whether it is benign or malignant.
An increased risk of developing phaeochromocytoma has been found in patients with MEN-1 and MEN-2 (multiple endocrine neoplasia types 1 and 2).
Many treatments interfere with the test result. Consult your doctor about all the medicines you are taking, as some will probably need to be stopped before the test. Smoking, coffee and foods containing caffeine (such as chocolate) also interfere with the result.
Is there anything else I should know?
Most phaeochromocytomas are located in the adrenal glands. However, plasma free metanephrines do not tell the doctor where the tumour is, or whether it is benign or malignant.
An increased risk of developing phaeochromocytoma has been found in patients with MEN-1 and MEN-2 (multiple endocrine neoplasia types 1 and 2).
Many treatments interfere with the test result. Consult your doctor about all the medicines you are taking, as some will probably need to be stopped before the test. Smoking, coffee and foods containing caffeine (such as chocolate) also interfere with the result.
1. Is it possible to have more than one phaeochromocytoma at a time?
2. Is the amount of free metanephrines in the plasma proportional to the size of the tumour?
3. Do I need to be careful about certain foods or drinks and lie down before the test?
1. Is it possible to have more than one phaeochromocytoma at a time?
Yes, especially if there are cases in the family. A patient may have phaeochromocytoma in both adrenal glands or occasionally in other sites as well.
2. Is the amount of free metanephrines in the plasma proportional to the size of the tumour?
No, it has more to do with the characteristics of the tumour. Sometimes a very small tumour can produce a large amount of metanephrines.
3. Do I need to be careful about certain foods or drinks and lie down before the test?
Opinions differ on this. However, catecholamine levels in the blood are affected by diet and stress. For the test to be accurate, certain substances must be avoided and the patient’s physical and psychological stress must be kept as low as possible.