When is a serotonin test ordered? What do the results mean

Do you suffer from mood swings, anxiety, depression, or unexplained digestive issues?Your doctor may recommend a Serotonin Test to assess the levels of this vital hormone in your body—commonly known as the "happiness hormone."In this comprehensive guide from Daleeli Medical, we explain what serotonin is, when its test is needed, and what high or low levels might reveal about your health.

What Is Serotonin?

Serotonin is a neurotransmitter and chemical hormone mainly produced in the digestive system (about 90%) and in the brain. It plays a vital role in:

Regulating mood and feelings of happiness
Sleep-wake cycles
Appetite and digestion
Blood vessel constriction
Body temperature regulation

Any imbalance in serotonin levels may lead to psychological or physical issues.

What Is the Serotonin Test?

The Serotonin Test is a blood or urine test used to measure serotonin levels in the body. It is often used to help diagnose conditions associated with high or low serotonin levels.

When Is the Serotonin Test Ordered?

Doctors may request this test in cases of:

✅ Suspected conditions such as:

Rare neuroendocrine tumors like carcinoid tumors, which secrete excessive serotonin
Chronic mental health symptoms such as depression or anxiety
Unexplained sleep or appetite disturbances
Digestive issues like chronic diarrhea or recurrent abdominal pain

Normal Serotonin Levels

In blood:
101–283 ng/mL
(Reference range may vary by lab and test method)
In urine (5-HIAA test):
Sometimes preferred over direct serotonin testing, especially for detecting serotonin overproduction over a 24-hour period.

What Does Low Serotonin Mean?

Low serotonin levels may indicate:

Psychological disorders:

Depression
Generalized anxiety disorder
Post-traumatic stress disorder (PTSD)
Sleep disorders such as insomnia

Other possible conditions:

Decreased appetite or eating disorders
Irritable bowel syndrome (IBS)
Fibromyalgia

Important Note:
The serotonin test alone is not sufficient to diagnose depression. It is used as a supportive tool alongside clinical and psychological evaluation.

What Does High Serotonin Mean?

High serotonin levels may be a sign of:

Carcinoid Syndrome:

A rare condition caused by tumors that secrete large amounts of serotonin, usually found in the gastrointestinal tract or lungs.

Common symptoms:

Persistent watery diarrhea
Facial flushing
Abdominal cramping
Heart valve issues

Serotonin Syndrome:

A potentially life-threatening condition caused by excessive serotonin levels, often due to combining multiple drugs that increase serotonin.

Common causes include:

SSRIs (Selective Serotonin Reuptake Inhibitors) like fluoxetine or sertraline
Tryptophan supplements
Certain opioids or recreational drugs

Symptoms include:

High fever
Shivering
Excessive sweating
Rapid heart rate
Confusion or seizures
Can lead to death if not treated promptly

How Is the Serotonin Test Performed?

A blood sample is drawn from a vein (usually in the morning)
Fasting for 8 hours is generally recommended
Patients should avoid certain foods for 3 days prior to the test, as they may affect serotonin levels:
- Bananas
- Pineapples
- Avocados
- Eggplants
- Tomatoes
- Walnuts

Is There an Alternative to Blood Serotonin Testing?

Yes. In cases of suspected carcinoid tumors, doctors may order a 24-hour urine test for 5-HIAA, a serotonin breakdown product, to assess long-term secretion levels.

❗ Is the Serotonin Test Enough to Diagnose Mental Disorders?

No.

The test cannot diagnose depression, anxiety, or other psychiatric conditions on its own
It is a supportive test used alongside clinical interviews and mental health evaluations
Results may be affected by diet, stress, or medication use

❓ Frequently Asked Questions (FAQ)

Does high serotonin mean extreme happiness?

No. Excess serotonin may actually indicate serious conditions like serotonin syndrome or neuroendocrine tumors.

Is serotonin linked to digestion?

Yes. Most serotonin is produced in the gut and plays a major role in bowel movements and appetite regulation.

What’s the difference between serotonin and 5-HIAA tests?

Serotonin test: measures serotonin in the blood
5-HIAA test: measures serotonin metabolite in urine and is better for detecting tumors

Can serotonin be increased naturally?

Yes, through:

Regular exercise
Sunlight exposure
A balanced diet rich in tryptophan (e.g., eggs, nuts, seeds)
Mindfulness, meditation, and relaxation techniques

✅ Summary

The Serotonin Test is a useful diagnostic tool for evaluating the body’s chemical balance. It may help uncover the cause of persistent mental, digestive, or hormonal symptoms.
High or low serotonin is not a disease in itself, but a clue to deeper underlying issues that require medical attention.

If your doctor orders this test, don’t worry—just follow the instructions carefully and discuss your results with a qualified specialist to get the right interpretation and treatment plan.