Summary
| Direction in Long COVID | ↑ Elevated — higher than in the comparison group |
|---|---|
| Category | Metabolic |
| Also described as | Tryptophan metabolite |
| Compared against | HC (healthy controls) |
| Associated symptoms | Neuroinflammation, fatigue |
| 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 |
Other conditions where Kynurenine is reported
- Kynurenine in ME/CFS — ↑ elevated vs HC
See the cross-condition hub: Kynurenine across conditions.
Trials, interventions and tests
In clinical-trial registrations this marker maps to the outcome term Hormonal levels (inluding tryptophan metabolites) (2 registered trials use a matching outcome measure).
Clinical trials using Kynurenine as an outcome
- NCT01040429: The Norwegian Study of Chronic Fatigue Syndrome in Adolescents: Pathophysiology and Intervention Trial (Completed)
Outcome measure: Hormonal levels (inluding tryptophan metabolites) - NCT06821087: Evaluating the Neuromodulatory Effect of Ketamine in Long COVID-19 (Enrolling By Invitation)
Outcome measure: Serum Biomarker Analysis
Interventions studied alongside this marker
Hypothesis-generating links from trial outcome usage and literature co-occurrence. Not treatment recommendations.
- Clonidine — 1 trial, 2 PubMed co-citations
e.g. Some central effects of kynurenic acid, 7-chlorokynurenic acid and 5,7- dichloro-kynurenic acid, glycine…
Related Metabolic markers in Long COVID
- TCA cycle intermediates ↑
- 5-Hydroxykynurenine ↑
- Histidine ↓
- Serotonin ↑
- Arginine ↓
- Putrescine ↑
- Glutamine ↓
- 5-Aminolevulinate ↑
Full list: Long COVID Biomarker Atlas.
Frequently asked questions
Is Kynurenine high or low in Long COVID?
Elevated. Studies summarised in the OSMF atlas report higher Kynurenine in Long COVID than in healthy controls. Source: Saito et al. 2024.
What symptoms is Kynurenine associated with in Long COVID?
The cited literature associates this marker with Neuroinflammation, fatigue. These are population-level associations and do not mean the marker causes the symptoms.
Which test measures Kynurenine?
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 Kynurenine result diagnostic of Long COVID?
No. No single biomarker is diagnostic of Long COVID. Kynurenine 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.
Is Kynurenine specific to Long COVID?
No. The same marker is also reported in ME/CFS in this atlas, so it reflects shared biology (for example inflammation or vascular stress) rather than a condition-specific signature.
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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.