What Is the Serotonin (SRT) Blood Test?

The Serotonin (SRT) Blood Test measures the level of serotonin present in your blood. Serotonin is a key neurotransmitter involved in mood regulation, emotional wellbeing, sleep patterns, appetite, digestion, and pain perception.

Although serotonin mainly acts within the brain and gastrointestinal system, blood measurements provide valuable insight into overall serotonin production and metabolism. This test is often used as part of mental health assessments, neurological investigations, and when abnormal serotonin activity is clinically suspected.

Why Do I Need a Test for Serotonin?

Serotonin imbalances can affect both mental and physical health. Low levels may contribute to mood changes, anxiety, sleep disruption, fatigue, and reduced stress resilience. Elevated levels, although less common, may indicate more serious underlying conditions that require medical follow-up.

You may benefit from serotonin testing if you experience persistent symptoms that are unexplained by routine blood tests or lifestyle factors, or if your clinician is investigating neurotransmitter-related causes of your symptoms.

Symptoms that may be linked to serotonin imbalance include:

• Low mood or depressive symptoms
• Anxiety or emotional instability
• Poor or disrupted sleep
• Chronic fatigue or low motivation
• Brain fog or difficulty concentrating
• Appetite changes or digestive discomfort
• Headaches or altered pain sensitivity

Testing provides objective biochemical data, helping guide further evaluation or monitoring where appropriate.

Benefits of the Serotonin (SRT) Blood Test

1. Provides objective insight into mood-related biochemistry
   Moves assessment beyond symptoms alone by measuring serotonin levels directly.
2. Supports investigation of anxiety and low mood
   Helps identify whether neurotransmitter imbalance may be contributing.
3. Assists in sleep and circadian rhythm assessment
   Serotonin plays a critical role in melatonin production and sleep regulation.
4. Aids evaluation of chronic fatigue and low energy
   Useful when tiredness is persistent and unexplained.
5. Adds depth to neurological and hormonal testing
   Complements other investigations for complex symptom profiles.
6. Can detect abnormal serotonin metabolism
   Identifies unusually low or high levels that may need further review.
7. Useful for monitoring changes over time
   Allows tracking alongside lifestyle or clinical interventions.
8. Processed using UK laboratory standards
   Results are aligned with recognised UK reference ranges.

Step-by-Step – How We Offer Serotonin Testing

Clinic appointment (UK-wide)
Choose your nearest UK clinic, attend your scheduled appointment, and a clinician will draw your blood sample. Results are delivered securely once available.

Home or hotel visit (+£60, UK-wide)
A qualified phlebotomist travels to your home, hotel, or workplace to collect your blood sample. You avoid travel and waiting rooms, making this option ideal for busy or private clients.

Both options are available across the UK.

Your Results Explained

Low serotonin levels

Low serotonin levels may indicate reduced neurotransmitter production or altered metabolism. This can be influenced by chronic stress, poor sleep, nutritional deficiencies, or certain medical conditions.

Low results are commonly associated with mood changes, anxiety, fatigue, and sleep disturbance. While blood serotonin does not directly measure brain serotonin activity, persistently low levels may warrant further clinical investigation.

Typical UK reference range:
Below approximately 50 ng/mL (laboratory dependent)

Normal serotonin levels

Results within the normal range suggest balanced systemic serotonin levels. However, normal results do not always exclude symptoms, as serotonin activity in the brain is influenced by receptors and signalling efficiency.

Normal levels are reassuring and often help rule out serotonin imbalance as a primary contributor to symptoms.

Typical UK reference range:
Approximately 50–220 ng/mL

High serotonin levels

Elevated serotonin levels are uncommon and may require prompt medical follow-up. High levels can be associated with rare conditions affecting serotonin production or breakdown.

Symptoms of excess serotonin may include agitation, gastrointestinal upset, sweating, rapid heart rate, or neurological symptoms.

Typical UK reference range:
Above approximately 220 ng/mL