The 5-hydroxyindoleacetic acid (5-HIAA) urine test is used to help diagnose and monitor carcinoid tumors. It may be ordered by itself or along with a blood serotonin and/or chromogranin A level. 5-HIAA is the primary metabolite of serotonin that is excreted in the urine. Concentrations of 5-HIAA may be significantly increased when a person has a carcinoid tumor that produces serotonin.
A 24-hour urine sample is preferred for the 5-HIAA test because the level of the metabolite 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 excess 5-HIAA is released intermittently, then it may be missed.
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 health practitioner 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 healthcare provider before decreasing or discontinuing any medications.
This article was last reviewed on May 28, 2014. | This article was last modified on October 29, 2015.
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