Other names: 5-HT; 5-Hydroxy Tryptamine

Serotonin is a chemical, which is produced from the amino acid tryptophan; it helps to regulate the constriction of blood vessels, transmit nerve impulses and controls moods. 90 percent of the serotonin in the blood is found in the platelets; it is produced when it is needed by the brain and other cells in the bronchial tubes and gastrointestinal tract. Serotonin is metabolised by the liver; the resulting metabolites are excreted in the urine.

When is the test used?

The test is used primarily to detect carcinoid tumours; the test is usually ordered if the patient has already had a 24 hour urine 5-HIAA test. The test is usually ordered when the patient has symptoms associated with carcinoid tumours.

How is the test done?

The test is done by collecting and analysing a sample of the patient’s blood; in most cases, a syringe is inserted into a vein on the inside of the elbow and the blood is drawn out using a syringe. When the doctor or nurse has a sufficient sample, the blood will be bottled, branded with the patient’s name and sent off to the laboratory for analysis.

What do the test results mean?

If levels of serotonin are higher than normal and the patient has symptoms of a carcinoid tumour, this indicates it is likely that the patient has a tumour; however, the result will not be sufficient to form a diagnosis and further tests, including scans and biopsies, will be ordered.

If levels of serotonin are normal and the patient does not have symptoms of a carcinoid tumour, it is unlikely that they have a tumour.

If levels of serotonin are normal but the patient has symptoms of a tumour, this may still indicate that they have a tumour and further tests will be required; some tumours do not produce serotonin.

Specific Blood Tests

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