Your doctor may have given you a pathology request form that includes tests for metanephrines or catecholamines. Not all patients are given the same instructions about preparing for these tests and there are some differences in how blood samples are collected. The following information may help you understand some of the reasons for this and help you get the best outcome for your situation.
Types of Tests
“Plasma free metanephrines” is the best test for diagnosing PPGLs. 24h urine fractionated metanephrines may be used as an alternative in some circumstances. Other tests used in the past include urine total metanephrines, plasma catecholamines, urinary catecholamines and urinary VMA.
The actual testing is only done at a small number of laboratories in Australia, so your blood collection centre will be sending your sample to one of these.
Diet
Plasma free metanephrines and urinary metanephrines are not affected by particular foods in your diet. Some other tests may be affected by diet, so follow all specific instructions.
Medications
This is a complex area and you must follow your doctor’s instructions. Don’t stop taking any medication because of something you have read or heard without speaking to your doctor first.
Fasting
Patients are to fast overnight and should not have coffee, tea, alcohol or tobacco on the morning of the test.
Exercise
Stress due to exercise can give a possible false positive result and some pathology labs might recommend not exercising prior to the test.
Lying Down
Prior to taking a blood sample for plasma free metanephrines, patients should fast overnight and, ideally, lie down for half an hour. Lying down is not always practical if the pathology collection rooms only have one room and other patients are waiting. If this is the case and your test results come back negative, it is safe to say that sitting up did not affect the outcome of this test. In a very small number of cases, sitting up may cause an otherwise negative test to be positive (false positive). Therefore, if your first test result is positive, another sample should be collected, this time after you have been lying down for half an hour.
There may be some things you can do to help have your blood collected lying down. Consider some of the following;
- Phone ahead or call in to the pathology collection centre a few days beforehand. It is often best to make an appointment for special collections such as this. Ask for any special instructions and whether you will be lying down.
- If there is only one collection centre where you live and you can’t lie down there, perhaps your GP has a room where this can be done. It may be possible for the GP and pathology company to work together on taking your blood and sending it to the laboratory.
- If you have a choice of collection centres, choose a large one with multiple rooms and blood collectors. These may be listed on the company’s website as Procedural Centres or something similar. Again, call ahead of time, make an appointment and ask for any special instructions.
