Serotonin
Also known as: 5-Hydroxy Tryptamine; 5-HT
Formal name: Serotonin
Related tests: 5-HIAA; Chromogranin A
The Test
How is it used?
Serotonin may be ordered along with, or following, a 24-hour urine 5-HIAA test to help diagnose carcinoid tumors. It is not generally used as a monitoring tool to evaluate the effectiveness of treatment or to detect recurrence of a carcinoid tumor. Monitoring tests may include 5-HIAA and Chromogranin A.
When is it ordered?
This test is primarily ordered when a patient has symptoms suggestive of a carcinoid tumor. It may be ordered initially or as a follow-up test when 5-HIAA test results are normal or near normal.
What does the test result mean?
A significantly increased level of serotonin in a patient with carcinoid syndrome symptoms is suggestive but not diagnostic of a carcinoid tumor. In order to diagnose the condition, the tumor itself must be located and biopsied. The doctor will frequently follow an abnormal test result with an order for an imaging scan to help locate any tumor(s) that may be present.
A patient with symptoms may still have a carcinoid tumor even if the concentrations of serotonin and 5-HIAA are normal. The patient may have a tumor that does not secrete serotonin or one that secretes it intermittently. A patient with no symptoms and normal or low levels of serotonin and 5-HIAA is unlikely to have a serotonin-secreting carcinoid tumor.
Is there anything else I should know?
There are a variety of drugs that can affect the serotonin test, including morphine, monoamine oxidase (MAO) inhibitors such as reserpine, methyldopa, and lithium. Patients should talk to their doctor before decreasing or discontinuing any medications.
Serotonin concentrations may be slightly increased in patients with intestinal obstructions, acute myocardial infarction (heart attack), cystic fibrosis, and dumping syndrome. The serotonin test is not usually ordered with these conditions.
