Hydroxyindoleacetic acid - 5HIAA

This test measures the amount of 5-hydroxyindoleacetic acid (5-HIAA) in the urine. 5-HIAA is a muscle stimulant and the primary metabolite of serotonin, a chemical derived from the amino acid tryptophan. In health, most serotonin is produced by the gastrointestinal (GI) tract where it regulates intestinal movements. The remainder is produced by the central nervous system where it functions to regulate mood, appetite and the wake/sleep cycle. After it has been used by the body, serotonin is broken down in the liver, and its metabolites, including 5-HIAA, are excreted in the urine. Normally, only small amounts of 5-HIAA is present in the urine. However, large quantities of serotonin and 5-HIAA may be produced by some carcinoid tumours.

Carcinoid tumours are typically slow-growing masses. The majority of carcinoid tumours form in the gastrointestinal tract but they can also form at other sites such as in the lungs and the pancreas. Many carcinoid tumours remain small and do not cause any symptoms. A small percentage of carcinoid tumours grow large enough to cause obstructions in the intestines or bronchial tubes of the lungs. Some carcinoid tumours can spread to other organs. The most common site of spread is to the liver.

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. This collection of symptoms is referred to as the carcinoid syndrome. Such symptoms will usually only appear after the tumour has spread to the liver. The serotonin that causes the 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 the 24-hour urine collection, all urine should be saved for a 24-hour period. It is better to keep sample in a cool dark place. When complete the sample is taken as soon as possible to your GP or the laboratory for preservation. Pre-sample preparation is important for accurate 5-HIAA test results.
For more information, see Common Questions, Is there anything else I should know below and talk to your doctor.

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 aubergine (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. It is important that those being tested talk to their healthcare provider before decreasing or discontinuing any medications.