Does this test have other names?
What is this test?
This test is sometimes used to help to diagnose carcinoid syndrome. This problem can
occur in people with carcinoid tumors. These tumors grow from a certain type of cell,
and they usually show up in the lungs, stomach, small intestine, rectum, and appendix.
Some carcinoid tumors can convert a substance made from an amino acid in the body
called tryptophan into a chemical called serotonin. Serotonin is further broken down
to 5-HIAA. 5-HIAA is the main test for carcinoid syndrome. But a blood test to measure
levels of serotonin in the blood is sometimes also used.
Relatively few carcinoid tumors—about 10% or less—are linked to carcinoid syndrome.
Usually these are tumors that grow in a certain part of the small intestine and spread
to the liver.
Why do I need this test?
You might have this test to find out whether you have a carcinoid tumor. Symptoms
of carcinoid tumor can include:
Severe skin flushing, usually in the upper body, head, and neck
Visible blood vessels in the skin, especially on the cheeks and neck
Diarrhea, possibly severe and with cramping
People with carcinoid syndrome may also have symptoms of heart valve disease and tightening
of the airways in the lungs.
What other tests might I have along with this test?
The main test for carcinoid syndrome measures a substance called 5-HIAA in the urine.
When a tumor makes serotonin, your body turns it into 5-HIAA. This test may require
collecting all the urine you make over a 24-hour period.
Another test measures a substance called chromogranin A in your blood. Higher levels
may point to a larger tumor size.
What do my test results mean?
A result for a lab test may be affected by many things, including the method the laboratory
uses to do the test. If your test results are different from the normal value, you
may not have a problem. To learn what the results mean for you, talk with your healthcare
Higher levels of serotonin in your blood may point to carcinoid syndrome. Research
found that people without carcinoid syndrome had serotonin levels in their blood of
71 to 310 nanograms per milliliter (ng/mL). In people with carcinoid syndrome, levels
were 790 to 4,500 ng/mL.
But eating foods rich in tryptophan such as avocados or bananas can cause a false-positive
result. For this reason, the serotonin test is not recommended for diagnosing carcinoid
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection,
bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight
stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Eating foods rich in tryptophan may cause tests to come back falsely high. These include:
How do I get ready for this test?
Avoid eating foods that can affect your test results (listed above) for at least 24
hours before the test. Tell your healthcare provider about any medicines you're taking.