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5-Hydroxytryptamine (Serotonin) in Serum or Plasma

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of serotonin, a chemical produced by your body that helps regulate mood, appetite, and sleep. It may be checked if you have symptoms linked to serotonin-related conditions or as part of a broader evaluation.

Quick summary

Serotonin levels can help diagnose or monitor conditions affecting mood, digestion, or blood clotting.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
25817-8
Short code
Xylose 1.5h p Xyl PO SerPl-sCnc
Synonyms
Xylose 1.5h p Xyl PO SerPl-sCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your healthcare provider may order a serotonin test if you have symptoms such as depression, anxiety, digestive issues (like irritable bowel syndrome), or unusual bleeding. It could also be part of testing for conditions like carcinoid syndrome or serotonin syndrome, or to assess serotonin-related medications.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it involves drawing blood, but this depends on your provider’s instructions. If you’re taking medications that affect serotonin, let your doctor know.

How the Test Is Performed

A healthcare professional will draw blood from a vein in your arm. The blood sample will be sent to a lab for analysis using a sensitive immunoassay method to detect serotonin levels.

What the Results Mean

Results are interpreted based on your overall health, symptoms, and medical history. Abnormally high or low serotonin levels may indicate underlying conditions that require further evaluation by your doctor.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Serotonin Level

Frequently asked questions

What Does a High Serotonin Level Indicate?
Elevated serotonin can be linked to conditions like carcinoid tumors (which release excess serotonin), serotonin syndrome (a rare but serious reaction to certain medications), or digestive disorders such as carcinoid syndrome. Your provider will consider other factors, like medications or symptoms, to diagnose the cause.
What Does a Low Serotonin Level Indicate?
Low serotonin levels may suggest deficiencies in mood regulation, digestive disorders (e.g., low serotonin due to gut issues), or rare genetic disorders. If serotonin is low due to medication (e.g., SSRIs), your provider may adjust treatment.
How Often Should I Get This Test?
This test is typically ordered as needed, depending on your symptoms or medical needs. Your doctor will determine how often to repeat it, if at all, based on your treatment plan and results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy