Summary
| Direction in Long COVID | ↓ Reduced — lower than in the comparison group |
|---|---|
| Category | Metabolic |
| Also described as | Amino acid |
| Compared against | R (recovered individuals without persistent symptoms) |
| Associated symptoms | Amino acid metabolism |
| 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 Neuropeptide Y (1 registered trials use a matching outcome measure).
Clinical trials using Histidine as an outcome
- NCT03496961: Yan Nian Jiu Zhuan Fa Improve Chronic Fatigue Syndromes (Unknown)
Outcome measure: Neuropeptide Y
Also sold as a nutrient or supplement
Histidine (amino acid). Amino acid supplement. This tag means the analyte is also available orally; it is not a product endorsement and a low or high level does not by itself justify supplementation.
Related Metabolic markers in Long COVID
- Arginine ↓
- TCA cycle intermediates ↑
- Glutamine ↓
- Kynurenine ↑
- Asparagine ↓
- 5-Hydroxykynurenine ↑
- Aspartate ↓
- Serotonin ↑
Full list: Long COVID Biomarker Atlas.
Frequently asked questions
Is Histidine high or low in Long COVID?
Reduced. Studies summarised in the OSMF atlas report lower Histidine in Long COVID than in recovered individuals without persistent symptoms. Source: Saito et al. 2024.
What symptoms is Histidine associated with in Long COVID?
The cited literature associates this marker with Amino acid metabolism. These are population-level associations and do not mean the marker causes the symptoms.
Which test measures Histidine?
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 Histidine result diagnostic of Long COVID?
No. No single biomarker is diagnostic of Long COVID. Histidine 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.