To help diagnose a carcinoid tumor that produces serotonin
Serotonin
When you have symptoms suggestive of a carcinoid tumor, such as flushing, diarrhea, and/or wheezing
A blood sample drawn from a vein in your arm
You may be instructed to avoid certain foods and medications prior to this test. (For more details, see the "What is being tested?" section.)
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How is the test used?
A serotonin test may be used to help diagnose carcinoid tumors. It may be ordered along with, or following, a 24-hour urine 5-HIAA test.
The serotonin test is not generally used as a monitoring tool to evaluate the effectiveness of treatment or to detect recurrence of a carcinoid tumor. Chromogranin A and 5-HIAA may be used for this purpose.
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When is it ordered?
This test is primarily ordered when you have symptoms suggestive of a carcinoid tumor.
Some signs and symptoms include:
- Flushing of the face and neck (appearance of deep red color, usually with sudden onset)
- Diarrhea, nausea, vomiting
- Rapid heart rate
- Wheezing, coughing, difficulty breathing
This test may be ordered initially or as a follow-up test when 5-HIAA test results are normal or near normal.
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What does the test result mean?
A significantly increased level of serotonin in a person 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, biopsied, and examined by a pathologist. The healthcare practitioner will frequently follow up an abnormal test result with an order for an imaging scan to help locate any tumor(s) that may be present.
You may still have a carcinoid tumor even if the concentrations of serotonin and 5-HIAA are normal. Some carcinoid tumors do not produce serotonin or only produce it intermittently.
If you have no symptoms and normal levels of serotonin and 5-HIAA, it is unlikely to have a serotonin-secreting carcinoid tumor.
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What drugs can affect the serotonin test?
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Should I have both the serotonin and 5-HIAA tests performed?
Serotonin and 5-HIAA offer complementary information. In some cases, 5-HIAA is preferred because it is more stable and, since it is collected for 24 hours, there is more chance of detecting increased 5-HIAA than in identifying excess serotonin that is only released intermittently. Talk to your healthcare practitioner about which tests are appropriate for your condition.
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Are some people at a higher risk for developing a carcinoid tumor?
Anyone at any age can develop a carcinoid tumor but, according to the American Cancer Society, the average age at diagnosis is the early 60s for GI carcinoid tumors and between age 45 and 55 for lung carcinoid tumors. If you have a family history of multiple endocrine neoplasia (MEN1), a genetic condition that increases a person's risk of developing tumors in the endocrine system glands, you may be at higher risk for developing a carcinoid tumor.
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How does a healthcare practitioner locate the carcinoid tumor?
This is usually accomplished through the use of imaging scans such as x-rays, computed tomography (CT), or magnetic resonance imaging (MRI). In some cases, surgery is required to find the tumor. For more on these imaging tests, visit RadiologyInfo.org.
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How does my healthcare practitioner tell whether a tumor is benign or cancerous?
In order to determine whether the tumor is benign or cancerous, your healthcare practitioner will need to perform a biopsy or remove the tumor surgically. The tumor is sent to the laboratory and a pathologist will examine the tumor cells using a microscope. (For more, see the article on Anatomic Pathology.)
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Is there anything else I should know?
Serotonin concentrations may be slightly increased in people with intestinal obstruction, acute myocardial infarction (heart attack), cystic fibrosis, and dumping syndrome. The serotonin test is not usually ordered with these conditions.