Why do 5-HIAA urine tests sometimes come back high and other times low after carcinoid tumors have been removed?

The urine 5-HIAA test for carcinoid is crude and can be strongly influenced by special diet and drugs. The patient must be on a special diet before and during the urine collection. Even then the test can miss up to 50% of the cases. It should not be relied on alone. Other markers for carcinoid tumor are blood serotonin, tryptophan, chromogranin A, pancreatic polypeptide and, of course, the OctreoScan.

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