This test measures the amount of 5-HIAA, the primary metabolite of serotonin, to help diagnose and monitor treatment for a serotonin-secreting carcinoid tumour.
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 are 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 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.
High-performance liquid chromatography
For the 24-hour urine collection, all urine should be saved for a 24-hour period. It is better to keep a sample in a cool dark place. Then put 30 ml aliquot from a 24-hour urine collection to the container provided (it contains 10 ml of 0.1N Hydrochloric Acid). When complete the sample should be taken as soon as possible to our laboratory for processing.
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. Drugs that can increase 5-HIAA include acetaminophen, caffeine, ephedrine (an ingredient found in some cough medicines), diazepam (Valium), nicotine, glyceryl guaiacolate (an ingredient found in some cough medicines), and phenobarbital. Drugs that can decrease 5-HIAA include aspirin, ethyl alcohol, imipramine, levodopa, MAO inhibitors, heparin, isoniazid, methyldopa, and tricyclic antidepressants. You should talk to their doctor before decreasing or discontinuing any medications.
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.
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