Understanding Your Laboratory Test: A Patient Guide to Preparation, Procedure, and Results

This is a laboratory test that helps your healthcare provider learn more about what is happening inside your body. The results can show how well certain organs are working, look for signs of illness, or help monitor a condition you already have.

The 5-Hydroxyindoleacetate (5-HIAA) test measures the amount of 5-HIAA in your urine. 5-HIAA is a breakdown product (metabolite) of serotonin, a hormone and neurotransmitter produced by your body. This test requires collecting all urine produced over a 24-hour period.

Your provider may order this test to help find the cause of symptoms you are having, to screen for a health problem before it causes symptoms, or to see how well a current treatment is working. The results help guide decisions about your ongoing care.

Your doctor may order this test if they suspect you have a carcinoid tumor, which is a rare type of neuroendocrine tumor. Carcinoid tumors often produce excess serotonin, leading to elevated 5-HIAA levels in urine. Symptoms that might prompt this test include flushing, diarrhea, abdominal cramps, and wheezing.

Preparation depends on the type of test being done. You may be asked to fast for 8 to 12 hours, drink extra water, or avoid certain medicines or supplements beforehand. Tell your provider about all medications you take, and follow the instructions you are given.

For 24-48 hours before and during the urine collection, avoid: bananas, avocados, walnuts, pecans, pineapples, tomatoes, and eggplant. Also avoid caffeine, alcohol, and certain medications including antidepressants (especially SSRIs), cough medicines, and blood pressure medications. Consult your doctor about which medications to temporarily stop.

Most laboratory tests use a small sample of blood drawn from a vein in your arm, although some use urine, saliva, or a swab from the mouth or throat. A trained technician collects the sample and sends it to a laboratory, and the process usually takes only a few minutes.

You will receive a special container for urine collection. On the morning of the test, start by urinating into the toilet (not into the container). After that, collect all urine in the container for the next 24 hours. Keep the container refrigerated or in a cool place. Return the container to the lab as instructed.

These tests are very safe. You may feel a quick sting when the needle goes in, and the site may be bruised or slightly sore for a day or two. Serious problems such as infection or heavy bleeding are rare. Contact your provider if discomfort or swelling gets worse.

This test has no physical risks. The main inconvenience is the need to collect all urine over 24 hours and keep it properly stored. Some people may find it slightly uncomfortable to carry the collection container with them.