Since my diagnosis last October, every six months I have to collect urine for twenty four hours. This is tested for 5-hydroxyindole acetic acid (5-HIAA), which is a metabolite or waste product of serotonin. Apparently if my carcinoid tumor has spread, it produces large amounts of serotonin. Serotonin syndrome or toxicity causes symptoms such as flushing, wheezing and diarrhea.
Testing for 5-HIAA frequently gives false positives. In my case, my results are border line normal. They aren’t increasing, but they are slightly above what my oncologist thinks are normal. I am a little puzzled by this as they are lower than those given in the first weblink above, but then I don’t know what units he is using. Fortunately I don’t have any of the symptoms of serotonin syndrome and all the other tests I had in July – various blood tests – came back as normal too. It is a bit nervewracking though not to be given the all clear. He actually said that as I am not showing any of the symptoms that we will not change the way we were currently managing my ex-carcinoid tumor status. It does mean more tests in January like this year, but I was expecting that anyway. Hopefully the results from these tests will reassure my oncologist and my above average levels can be accepted as normal in the future.
So why does this test give so many false positives? The consumption of many foods, including bananas, pineapples, red plums, tomatoes and walnuts, increases the urinary levels of 5-HIAA because they have a naturally high serotonin content. Bananas, for example, have 15 micrograms of serotonin per gram weight [it doesn’t say whether it is wet or dried weight in the article], tomatoes have 3.2 and English walnuts have a staggering 87 micrograms/gram.
Does this mean we also benefit from the serotonin when we eat these fruit and veg? Unfortunately, dietary serotonin is converted to 5-HIAA in the intestinal mucosa and liver.
JM Feldman and EM Lee (1985): Serotonin content of foods: effect on urinary excretion of 5-hydroxyindoleacetic acid. Amer. J. Clin. Nutr. 42 (4) 639-643