Understanding Your Laboratory Test: A Patient Guide to Testing and Results

This is a laboratory test that helps your doctor learn important information about your health. A small sample, such as blood, urine, or another body fluid or tissue, is collected and analyzed in a lab. The results give your care team a clearer picture of how your body is working and can help detect, diagnose, or monitor a medical condition.

The 5-Hydroxyindoleacetate (5-HIAA) urine test measures the amount of 5-HIAA in your urine. 5-HIAA is a breakdown product (metabolite) of serotonin, a hormone and neurotransmitter that helps regulate mood, sleep, and other bodily functions. This test requires collecting all urine produced over a 24-hour period.

Your doctor may order this test for several reasons, such as to look into symptoms you are having, to confirm or rule out a diagnosis, to screen for a condition before symptoms appear, or to see how well a treatment is working. It may also be part of a routine checkup to make sure everything looks normal.

Doctors order this test primarily to screen for and monitor carcinoid tumors. Carcinoid tumors are rare, slow-growing neuroendocrine tumors that can develop in various parts of the body, commonly in the gastrointestinal tract or lungs. These tumors often produce excess serotonin, which breaks down into 5-HIAA and appears in urine.

Preparation depends on the type of test, and your care team will give you specific instructions. In general, drink plenty of water unless told otherwise, wear a top with sleeves that roll up easily if blood will be drawn, and tell your doctor about all medicines, vitamins, and supplements you take. Some tests require fasting or temporarily stopping certain medicines, so follow your instructions carefully.

Proper preparation is crucial for accurate results. You should avoid the following for 48 hours before and during the urine collection: bananas, avocados, walnuts, pecans, pineapples, tomatoes, kiwi fruit, plums, eggplants, and certain medications including antidepressants, cough medicines, and blood pressure medications. Always inform your doctor about all medications and supplements you are taking.

The test is usually done in a doctor's office, clinic, hospital, or laboratory. A trained health professional will collect the needed sample, for example by drawing blood from a vein in your arm, asking you to provide a urine sample, or taking a small swab. The sample is then sent to a laboratory for analysis, and your doctor will review the results with you and explain what they mean.

You will receive a special container for urine collection. On the day of collection, start by urinating into the toilet upon waking up. For the next 24 hours, collect all urine in the provided container, including the final morning specimen on day two. Keep the container refrigerated or in a cool place during collection. Return the completed collection to your laboratory as instructed.