Prognostic value of 5-hydroxyindoleacetic acid (5-HIAA)

Urinary 5-HIAA, the primary metabolite of serotonin, has both diagnostic and prognostic value in NETs associated with carcinoid syndrome.1-3 5-HIAA is measured by high-precision liquid chromatography in a 24-hour urine sample.4

Elevated levels of 5-HIAA have been associated with poor outcomes5 and the development of carcinoid heart disease.6 Reductions in 5-HIAA are correlated with relief of carcinoid symptoms and disease stabilization.7

Considerations when ordering 5-HIAA testing

5-HIAA is only elevated in NETs/metastases that secrete serotonin. It may not be a useful marker in other NETs.1

5-HIAA may be increased by ingestion of foods high in serotonin, such as avocados, bananas, pineapples, walnuts, and kiwifruit.2 Certain medications, including guaifenesin, acetaminophen, salicylates, and L-dopa, may also affect 5-HIAA. Patients should be instructed to avoid these foods and medications before and during urine collection.2