5-HIAA

5-HIAA may be requested by itself and sometimes with blood serotonin to help diagnose and monitor carcinoid tumours. A 24-hour urine sample is preferred for the 5-HIAA test because the metabolite level in the urine can vary during the day. In exceptional situations 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 requested when a patient has symptoms suggestive of a carcinoid tumour. It may also be ordered at intervals to help monitor the effectiveness of treatment in patients who have been diagnosed with and treated for a serotonin-secreting carcinoid tumour.

A significantly increased level of 5-HIAA in a 24-hour urine sample in a patient with carcinoid syndrome symptoms is suggestive but not diagnostic of a carcinoid tumour. In order to diagnose the condition, the tumour itself must be located and a sample of it examined. The doctor will frequently ask to repeat the sample collection and test following an abnormal test result before requesting an imaging scan to help locate any tumour(s)that may be present.

A patient with symptoms may still have a carcinoid tumour even if the concentration f 5-HIAA is normal. The patient may have a tumour that does not secrete serotonin or one that secretes it intermittently. A patient with no symptoms and normal levels of 5-HIAA is unlikely to have a serotonin-secreting carcinoid tumour.

In patients who are being monitored following treatment for carcinoid tumour, decreasing levels of 5-HIAA indicate a response to treatment, while increasing or continued excessive concentrations indicate that the treatment has not been successful.

Foods such as avocados, bananas, pineapples, plums, walnuts, tomatoes, kiwi fruit, eggplant and health food supplements containing 5-hydroxytrytophen can increase 5-HIAA and should be avoided for three 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. Patients should talk to their doctor before decreasing or discontinuing any medications.