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Serotonin blood test

5-HT level; 5-hydroxytryptamine level; Serotonin test

The serotonin test measures the level of serotonin in the blood.

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How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

No special preparation is needed.

How the Test will Feel

When the needle is inserted to draw blood, some people feel slight pain. Others feel a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

Serotonin is a chemical produced by nerve cells.

This test is usually done when carcinoid syndrome is suspected. Carcinoid syndrome is a group of symptoms associated with carcinoid tumors. These are tumors of the small intestine, colon, appendix, and bronchial tubes in the lungs. People with carcinoid syndrome often have high levels of serotonin in the blood.

Normal Results

The normal range is 50 to 200 ng/mL (0.28 to 1.14 µmol/L).

Note: Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your health care provider about the meaning of your specific test results.

What Abnormal Results Mean

A higher-than-normal level may indicate carcinoid syndrome.

Risks

There is little risk in having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Related Information

Carcinoid syndrome
Tryptophan

References

Siddiqi HA, Rabinowitz S, Axiotis CA. Laboratory diagnosis of gastrointestinal and pancreatic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 23.

Wolin EM, Jensen RT. Neuroendocrine tumors. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 219.

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Review Date: 2/28/2023  

Reviewed By: Jacob Berman, MD, MPH, Clinical Assistant Professor of Medicine, Division of General Internal Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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