Summary
| Direction in Long COVID | ↑ Elevated — higher than in the comparison group |
|---|---|
| Category | Metabolic |
| Also described as | 5-HT |
| Compared against | HC (healthy controls) |
| Associated symptoms | Mood, GI symptoms |
| Test type | Blood test (serum / plasma / whole blood) |
| Source | Saito et al. 2024 — doi:10.3389/fimmu.2024.1341843 |
| Condition atlas | Long COVID Biomarker Atlas |
Trials, interventions and tests
In clinical-trial registrations this marker maps to the outcome term To compare alterations in hormonal components (Serotonin) among the three treatment arms. (2 registered trials use a matching outcome measure).
Clinical trials using Serotonin as an outcome
- NCT06766825: Study to Evaluate the Efficacy and Safety of Plitidepsin in Adults With Post-COVID-19 Condition (PCC) (Recruiting)
Outcome measure: To compare alterations in hormonal components (Serotonin) among the three treatment arms. - NCT06620406: Synbiotic Therapy for NP-PASC (Completed)
Outcome measure: Difference in other biomarkers between study arms
Related Metabolic markers in Long COVID
- 5-Hydroxykynurenine ↑
- Putrescine ↑
- Kynurenine ↑
- 5-Aminolevulinate ↑
- TCA cycle intermediates ↑
- Porphobilinogen ↑
- Histidine ↓
- Uracil ↓
Full list: Long COVID Biomarker Atlas.
Frequently asked questions
Is Serotonin high or low in Long COVID?
Elevated. Studies summarised in the OSMF atlas report higher Serotonin in Long COVID than in healthy controls. Source: Saito et al. 2024.
What symptoms is Serotonin associated with in Long COVID?
The cited literature associates this marker with Mood, GI symptoms. These are population-level associations and do not mean the marker causes the symptoms.
Which test measures Serotonin?
It is measured as a blood test (serum / plasma / whole blood). Many of the cited studies used research-grade assays, so clinical availability may vary.
Is one abnormal Serotonin result diagnostic of Long COVID?
No. No single biomarker is diagnostic of Long COVID. Serotonin findings come from group comparisons, overlap considerably between patients and controls, and vary with study design, timing and comparison group. A result should be interpreted by a clinician alongside symptoms, history and other tests.
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Last reviewed: 2026-06-29 · Page generated from long-covid.json · Browse: Long COVID atlas · Biomarker Index · All marker pages
Disclaimer: This page is an educational synthesis of published, peer-reviewed research and is not medical advice. Biomarker findings vary across studies with case definitions, comparison groups, timing and assay methods. Direction of change reflects the predominant finding in the cited source and does not establish a diagnostic threshold. Discuss any test result with a qualified clinician.