Summary
| Direction in Long COVID | ↑ Elevated — higher than in the comparison group |
|---|---|
| Category | Metabolic |
| Also described as | Kynurenine pathway |
| Compared against | HC (healthy controls) |
| Associated symptoms | Neurotoxic metabolite pathway |
| 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 Serum Biomarker Analysis (1 registered trials use a matching outcome measure).
Clinical trials using 5-Hydroxykynurenine as an outcome
- NCT06821087: Evaluating the Neuromodulatory Effect of Ketamine in Long COVID-19 (Enrolling By Invitation)
Outcome measure: Serum Biomarker Analysis
Related Metabolic markers in Long COVID
- Kynurenine ↑
- Serotonin ↑
- TCA cycle intermediates ↑
- Putrescine ↑
- Histidine ↓
- 5-Aminolevulinate ↑
- Arginine ↓
- Porphobilinogen ↑
Full list: Long COVID Biomarker Atlas.
Frequently asked questions
Is 5-Hydroxykynurenine high or low in Long COVID?
Elevated. Studies summarised in the OSMF atlas report higher 5-Hydroxykynurenine in Long COVID than in healthy controls. Source: Saito et al. 2024.
What symptoms is 5-Hydroxykynurenine associated with in Long COVID?
The cited literature associates this marker with Neurotoxic metabolite pathway. These are population-level associations and do not mean the marker causes the symptoms.
Which test measures 5-Hydroxykynurenine?
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 5-Hydroxykynurenine result diagnostic of Long COVID?
No. No single biomarker is diagnostic of Long COVID. 5-Hydroxykynurenine 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.