At a glance
Also known as
5-hydroxyindoleacetic acid; HIAA; serotonin metabolite
Why get tested?
To help diagnose and monitor a serotonin-secreting
When to get tested?
When you have symptoms suggestive of a carcinoid tumour such as flushing, diarrhoea, and/or wheezing, and at intervals following treatment
Aurine sample; preferably a 24 hour urine sample
Test preparation needed?
You may be instructed to avoid certain foods and medications prior to this test.
What is being tested?
This test measures the amount of 5-hydroxyindoleacetic acid (5-HIAA) in the urine. 5-HIAA is the primary of serotonin, a hormone made from the tryptophan. Serotonin is produced as needed by the nervous system, mainly the brain, but also cells in the bronchial tubes (lungs) and gastrointestinal tract. It helps transmit nerve impulses and constrict blood vessels, participates in the wake-sleep cycle and affects mood. After it is used by the body, serotonin is broken down in the liver, and its metabolites, including 5-HIAA, are excreted in the urine.
Ordinarily, only small varying amounts of 5-HIAA are present in the urine. Large quantities of serotonin and 5-HIAA may be produced, however, by some . Carcinoid tumours are slow-growing masses found in the gastrointestinal tract, particularly the appendix and also in the lungs. The can be cancerous or noncancerous. They can remain small and not cause any symptoms. When carcinoid tumours are discovered in patients without symptoms during surgical procedures performed for other reasons, they are called ‘incidental’ tumours. A small percentage of these tumours may eventually grow large enough to cause obstructions in the intestines or bronchial tubes of the lungs.
About 10% of carcinoid tumours, primarily those found in the gastrointestinal tract, will produce enough serotonin to cause symptoms such as flushing of the face, diarrhoea, a rapid heart rate and wheezing, . These symptoms are referred to as carcinoid syndrome. The serotonin that causes carcinoid syndrome may be released continuously or intermittently and can lead to significantly increased quantities of 5-HIAA in the urine.
How is the sample collected for testing?
For a , all of the urine produced in a 24-hour period should be saved. It is best to keep the sample in a cool, dark place, such as a refrigerator.
Is any test preparation needed to ensure the quality of the sample?
Pre-sample preparation is important for accurate 5-HIAA test results. Foods such as avocados, bananas, pineapples, plums, walnuts, tomatoes, kiwi fruit and eggplant can interfere with 5-HIAA measurement and should be avoided for 3 days prior to and during urine collection. There are also a variety of drugs that can affect the 5-HIAA test, but you should talk to your doctor before decreasing or discontinuing any medications.