How is it used?When is it ordered?What does the test result mean?Is there anything else I should know?
This test is primarily ordered when a patient has symptoms suggestive of a
carcinoid tumor. 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 tumor.
What does the test result mean?NOTE: This test has no single number that identifies an abnormal result.
Your lab report (see a sample report) should include
a range of numbers (reference range) that identifies what is expected for you based on
your age, sex, and the method used in that laboratory. You can find more information
about expected results at Reference Ranges
and What They Mean. Lab Tests Online strongly recommends that you discuss the meaning of your test results with your doctor.
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 tumor. In order to diagnose the condition, the tumor itself must be located and a sample of it examined. 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.
A patient with symptoms may still have a carcinoid tumor even if the concentration of 5-HIAA is normal. The patient may have a tumor 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 tumor.
In patients 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.
Is there anything else I should know?
There are also 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. Patients should talk to their doctor before decreasing or discontinuing any medications.
