Understanding Your Laboratory Test: A Patient Guide to Testing, Preparation, and What the Results Mean

This test is a laboratory analysis performed on a sample from your body, such as blood, urine, or other tissue, to measure specific substances and help your healthcare provider evaluate how well your body is functioning and detect any conditions that may need further attention.

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

Your doctor may order this test to look for signs of illness, monitor a condition you already have, check how well a treatment is working, or include it as part of a routine checkup, because the results provide important information that helps guide decisions about your care.

Your doctor may order this test if they suspect you have a neuroendocrine tumor, such as carcinoid tumors or pheochromocytoma. These tumors can produce excess serotonin, leading to elevated 5-HIAA levels in urine. Symptoms that might prompt testing include flushing, diarrhea, abdominal pain, or heart palpitations.

Preparation depends on the specific test ordered, so follow your provider's instructions closely; you may be asked to fast for 8 to 12 hours, avoid certain foods, drinks, or medications, stay well hydrated, and tell your provider about all prescription drugs and supplements you currently take.

Proper preparation is crucial for accurate results. For 48 hours before and during the collection period, you should avoid: bananas, avocados, pineapples, plums, walnuts, and certain medications including antidepressants, cough medicines, and pain relievers. Your doctor will provide a complete list of items to avoid.

A trained healthcare professional will collect the needed sample, usually by drawing a small amount of blood from a vein in your arm using a sterile needle, and the sample is then sent to a laboratory where specialized equipment measures the values being tested before your provider reviews the results with you.

You will receive a special container for urine collection. On the morning of collection, start by urinating into the toilet and noting the time. Collect all subsequent urine in the container for the next 24 hours, including the first morning urine the next day. Keep the container refrigerated during collection. Return the completed collection to your lab as instructed.