Certain foods like pineapple, kiwi, banana, walnuts and drugs such as acetaminophen, nicotine or caffeine are known to interfere with the measurement.

[2][3][1] 5-HIAA levels can vary depending on other complications, including tumors, kidney malfunction, and small bowel resection.

Values greater than 25 mg per 24 hours (higher if the patient has malabsorption) are strong evidence for carcinoid.

Foregut tumors lack the decarboxylase enzyme necessary to convert 5-hydroxytryptophan to serotonin, resulting in minimal to no elevation in urinary 5-HIAA levels.

Tumors derived from hindgut cells (rectal carcinoid) rarely produce excess serotonin or 5-HIAA.