Serotonin blood test
Quick answer: This test measures serotonin, a chemical messenger, in your blood. It is mainly ordered, often with a urine 5-HIAA test, when a carcinoid (neuroendocrine) tumour is suspected.
- SampleBlood
- TakesAbout 5 minutes
- Before the testSome foods and medicines can affect the result, so follow the lab's instructions and tell your doctor what you take.
How the test is done
- 1You follow any diet or medicine instructions from the lab
- 2A vein in your arm is cleaned
- 3Blood is drawn into a tube and handled carefully
- 4A urine 5-HIAA test may be done at the same time
What your results can mean
Reading your report
Normal ranges differ between labs, so compare your result with the range printed on your report and discuss it with your doctor.
If the result is outside the usual range
A high level can point to a carcinoid (neuroendocrine) tumour, and can also be raised by foods such as bananas, pineapple, tomatoes and nuts, or by some medicines. A normal level does not fully rule out such a tumour.
Who usually has this test
People with flushing, diarrhoea, wheezing or a racing heart that suggest carcinoid syndrome, and those being followed after a neuroendocrine tumour.
Risks and aftercare
You can return to your usual diet after the sample unless the lab asks for more samples.
Names and options
Also called: serum serotonin, 5-HT test
Listed by the hospital as
- SEROTONIN, SERUM
Questions about this test
What is carcinoid syndrome?
Carcinoid syndrome is a group of symptoms such as flushing, diarrhoea and wheezing caused by hormones released from some neuroendocrine tumours. It is uncommon.
Which foods can affect a serotonin test?
Foods such as bananas, pineapple, kiwi, plums, tomatoes, avocados and walnuts can raise serotonin and related substances. The lab may ask you to avoid them for a few days before.
Is the blood serotonin test the main test for carcinoid tumours?
Urine 5-HIAA and blood chromogranin A are more commonly used. Blood serotonin may be added in some cases to help with diagnosis.
Related tests
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.