5-HIAA

This test measures the amount of 5-hydroxyindoleacetic acid (5-HIAA) in the urine. 5-HIAA is the primary metabolite of serotonin, a hormone derived from the amino acid tryptophan. Serotonin is produced as needed by the nervous system, mainly the brain, but also special cells in the bronchial tubes (lungs) and gastrointestinal (GI) 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 tumors. Carcinoid tumors are slow-growing noncancerous or cancerous neuroendocrine masses that can form in the GI tract, on the appendix, and in the lungs. About 2 out of every 3 carcinoids are found in the GI tract with most of the rest occurring in the lungs, though they may affect other organs as well. According to the American Cancer Society, there are about 11,000 to 12,000 neuroendocrine tumors or cancers diagnosed each year in United States. Many more of these tumors may exist, but most remain small and do not cause any symptoms. When carcinoid tumors are discovered in asymptomatic patients during surgical procedures performed for other reasons, they are called "incidental" tumors. A small percentage of these tumors may eventually grow large enough to cause obstructions in the intestines or bronchial tubes of the lungs.
About 10% of carcinoid tumors, primarily those found in the GI tract with liver involvement, will produce enough serotonin to cause symptoms, such as flushing of the face, diarrhea, a rapid heart rate, and wheezing, which 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.

For the 24-hour urine collection, all of the urine should be saved for a 24-hour period. It is best to keep the sample in a cool, dark place, such as a refrigerator.

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.

5-HIAA may be ordered by itself or along with a blood serotonin level to help diagnose and monitor carcinoid tumors. A 24-hour urine sample is preferred for the 5-HIAA test because the metabolite level in the urine can vary during the day. A random urine sample is sometimes tested, usually along with a urine creatinine level, when a 24-hour sample is not feasible. The random sample is not as accurate, however, and if the excess 5-HIAA is released intermittently, then it may be missed.

This test is primarily ordered when a person has symptoms suggestive of a carcinoid tumor. Examples of symptoms include:

• Flushing of the face and neck (appearance of deep red color, usually with sudden onset)
• Diarrhea, nausea, vomiting
• Rapid heart rate
• Wheezing, coughing, difficulty breathing

This test may also be ordered at intervals to help monitor the effectiveness of treatment in people who have been diagnosed with and treated for a serotonin-secreting carcinoid tumor.

A significantly increased level of 5-HIAA in a 24-hour urine sample in a person with carcinoid syndrome symptoms is suggestive but not diagnostic of a carcinoid tumor. In order to diagnose the condition, the tumor itself must be located and a sample of it examined (biopsy). The doctor will frequently follow an abnormal test result with an order for an imaging scan to help locate any tumor(s) that may be present. Someone with symptoms may still have a carcinoid tumor even if the concentration of 5-HIAA is normal. The person may have a tumor that does not secrete serotonin or one that secretes it intermittently. A person with no symptoms and normal levels of 5-HIAA is unlikely to have a serotonin-secreting carcinoid tumor.
In those who are being monitored following treatment for carcinoid tumor, decreasing levels of 5-HIAA indicate a response to treatment, while increasing or continued excessive concentrations indicate that the treatment has not been successful.

There are a variety of drugs that can affect the 5-HIAA test. Medications that can increase 5-HIAA include acetaminophen, caffeine, ephedrine, diazepam (Valium), nicotine, glyceryl guaiacolate (an ingredient found in some cough medicines), and phenobarbital. Medications that can decrease 5-HIAA include aspirin, ethyl alcohol, imipramine, levodopa, MAO inhibitors, heparin, isoniazid, methyldopa, and tricyclic antidepressants. People should talk to their doctor before decreasing or discontinuing any medications. 

 

Common Questions

1. Why do I have to collect my urine for 24 hours?
2. Are there other metabolites of serotonin?
3. Will my results be accurate if I must continue to take my medication?
4. Are some people at a higher risk for developing a carcinoid tumor?

1.  Why do I have to collect my urine for 24 hours?

2.  Are there other metabolites of serotonin?

3.  Will my results be accurate if I must continue to take my medication?

4.  Are some people at a higher risk for developing a carcinoid tumor?

 

source : http://www.labtestsonline.org/understanding/analytes/5hiaa/test.html