Use of certain drugs (e.g., chlorpromazine, promazine, imipramine, isoniazid, monoamine oxidase inhibitors, methenamine, methyldopa, phenothiazines, promethazine)
Renal insufficiency (possible)
Limitations
Foods rich in serotonin and medications, over-the-counter drugs, and herbal remedies that may affect metabolism of serotonin must be avoided at least 72 hours before and during collection of urine for 5-HIAA.
Twenty-four " hour collections are generally recommended, but random collections may be used. Refrigeration is the most important aspect of specimen preservation.
Urinary 5-HIAA is increased with malabsorption, in 75% of cases, usually when a carcinoid tumor is far advanced (with large liver metastases, often 300 " 1,000 mg/day), but may not be increased despite massive metastases.
Sensitivity is 73%.
The test is useful in the diagnosis of only 5 " 7% of patients with carcinoid tumors but in approximately 45% of those with liver metastases.
Disease extent and prognosis correlate generally with urine 5-HIAA excretion, and the level becomes normal after successful surgery. If urine HIAA is normal, the blood level of serotonin or a precursor, 5-hydroxytryptophan should be checked.