How is it used?
Catecholamine testing is mainly used to help detect and rule out
phaeochromocytomas in patients with symptoms. It also may be used to help monitor the effectiveness of treatment when a phaeochromocytoma is discovered and removed and to look for recurrence. The blood test is most useful when a patient has persistent high blood pressure or is experiencing an episode of hypertension. It is important to measure the hormone when a patient has symptoms because the hormones do not linger in the blood; they are used by the body, metabolised, and/or removed in the urine. Urine catecholamine testing measures the total amount of catecholamines released over a 24 hour period. Since the hormone levels may vary during this period, the urine test may detect excess production that is missed with the blood test. Blood and urine tests may be used together or separately and/or with urine and/or plasma metanephrines to look for very high levels of both catecholamines and their metabolites.
Since these tests are can be affected by drugs, foods, and stresses, there will be a certain number of
false positives. For this reason, catecholamine testing is not recommended as a screen for the general public. Doctors will frequently investigate a positive result by looking at a patient’s stresses, food and drug intake, then work to reduce any influences, and repeat the test to see whether the change(s) have been effective.
Occasionally, the tests may be used on an
asymptomatic person if an adrenal or neuroendocrine tumour is found on 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).
^ Back to top
When is it requested?
Catecholamine testing is used when a doctor either suspects that a patient has a phaeochromocytoma or wants to rule out the possibility. The doctor may request it when a patient has persistent or recurring high blood pressure with symptoms such as headaches, sweating, flushing, and rapid heart rate. It may also be ordered when a patient has high blood pressure that does not respond to treatment (patients with a phaeochromocytoma are frequently resistant to normal drugs).
Occasionally, the test may be used when an adrenal tumour is found by accident following a scanning procedure 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.
^ Back to top
What does the test result mean?
Since the catecholamine test is sensitive to many outside influences and phaeochromocytomas are rare, a doctor may see more
false positives with this test than true positives. If a symptomatic patient has large amounts of catecholamines in their blood and/or urine, further investigation is indicated. Serious illnesses and stresses can cause moderate to large temporary increases in catecholamine levels. Doctors must evaluate the patient as a whole - his or her physical condition, emotional state, medicines, and diet. When interfering substances and/or conditions are found and resolved, the doctor will frequently re-test the patient to determine whether the catecholamines are still high. The doctor may also request blood and/or urine metanephrine testing to help confirm the findings and imaging tests (such as an
MRI scan) to help find the tumour(s).
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.
If the concentrations of catecholamines are normal in both the plasma and urine, then it is unlikely that a patient has a phaeochromocytoma. Phaeochromocytomas do not necessarily produce catecholamines at a constant rate, however. If the patient has not had a recent episode of hypertension, their plasma and urine concentrations of catecholamines could be at normal or near normal levels even when a phaeochromocytoma is present.
^ Back to top
Is there anything else I should know?
While plasma and urine catecholamine testing can help detect and diagnose phaeochromocytomas, they cannot tell the doctor where the tumour is, whether there is more than one, or whether or not the tumour is
benign (although most are). The amount of catecholamines produced does not necessarily correspond to the size of the tumour. This is a physical characteristic of the tumour tissue. The total amount of catecholamines produced will tend to increase, however, as the tumour increases in size.
It is very important to talk to your doctor before discontinuing any prescribed drugs. The doctor will work with you to identify interfering substances and drug treatments to find out which of them can be safely interrupted and which must be continued for your well-being.
Some of the substances that can interfere with catecholamine testing include: paracetamol (acetaminophen), aminophylline, amphetamines, appetite suppressants, coffee, tea, and other forms of caffeine, chloral hydrate, clonidine, dexamethasone, diuretics, adrenaline, ethanol (alcohol), insulin, imipramine, lithium, methyldopa, MAO (monoamine oxidase) inhibitors, ACE inhibitors, nicotine, nitroglycerin, propafenone, reserpine, salicylates, theophylline, tetracycline, tricyclic antidepressants, and vasodilators.
The effects of these drugs on catecholamine results will be different from patient to patient and are often not predictable. Bananas and capsicums may also cause falsely elevated catecholamine results and should be avoided for 24 hours before and during the urine collection.
^ Back to top
