Summary
| Direction in Long COVID | ↑ Elevated — higher than in the comparison group |
|---|---|
| Category | Inflammatory |
| Also described as | Pro-inflammatory cytokine |
| Compared against | HC, R (healthy controls, recovered individuals without persistent symptoms) |
| Associated symptoms | Fatigue, systemic inflammation |
| Test type | Blood test (serum / plasma / whole blood) |
| LOINC code | 26881-5 |
| Source | Lai et al. 2023 — doi:10.3389/fmed.2023.1085988 |
| Condition atlas | Long COVID Biomarker Atlas |
Other conditions where Interleukin-6 (IL-6) is reported
- Interleukin-6 (IL-6) in Gulf War Illness — ↑ elevated vs HGV
- IL-6 in Low Back Pain — ↑ elevated vs chronic nonspecific LBP vs asymptomatic controls
- Interleukin-6 (IL-6) in Lyme Disease — ↑ elevated vs HC
- IL-6 in Major Depressive Disorder — ↑ elevated vs females with depression vs healthy female controls
- Interleukin-6 (IL-6) in ME/CFS — ↕ inconsistent vs HC
- IL-6 in PACVS — ↑ elevated vs HC
- IL-6 in Rheumatoid Arthritis — ↑ elevated vs RA vs healthy (established inflammatory pathway/drug target)
See the cross-condition hub: Interleukin-6 (IL-6) across conditions.
Trials, interventions and tests
In clinical-trial registrations this marker maps to the outcome term Interleukin-6 (IL-6) (12 registered trials use a matching outcome measure).
Clinical trials using Interleukin-6 (IL-6) as an outcome
- NCT06142253: Water-based Activity to Enhance Recovery in Long COVID-19 (Recruiting)
Outcome measure: Change in Blood labs - NCT07278206: Brain Stimulation in Long COVID (Recruiting)
Outcome measure: Interleukin-6 (IL-6) - NCT05524532: Effects of Immulina TM Supplements With PASC Patients (Completed)
Outcome measure: Plasma IL-6 (Interleukin 6, pg/mL) - NCT06597682: Evaluating Immunomodulatory Interventions in Post-Acute Sequelae of SARS-CoV-2 InfEction (Not Yet Recruiting)
Outcome measure: Change in IL-6 Levels - NCT06073002: Effects of a Home-Based Exercise Intervention in Subjects with Long COVID (Active Not Recruiting)
Outcome measure: Change of interleukin-6 (IL-6 measured in pg/ml) - NCT06064838: Effects of Cacao Flavonoids in Long COVID-19 Patients (FLALOC) (Completed)
Outcome measure: Interleukin-6 - NCT05356936: Pilot Study of Vitamin K2 (MK-7) and Vitamin D3 Supplementation and the Effects on PASC Symptomatology and Inflammatory Biomarkers (Completed)
Outcome measure: Change in interleukin 6 (IL-6) as measured by blood test - NCT04751669: Efficacy of a Dietary Supplementation in Reducing Hospital Admissions for COVID-19. Randomized Clinical Trial (Completed)
Outcome measure: Inflammatory parameters
4 more trials reference this marker.
Interventions studied alongside this marker
Hypothesis-generating links from trial outcome usage and literature co-occurrence. Not treatment recommendations.
- Exercise therapy — 2 trials, 6 PubMed co-citations
e.g. Concurrent improvement of cardiorespiratory fitness and modulation of inflammatory markers via 12-week… - Repetitive Transcranial Magnetic Stimulation — 1 trial, 6 PubMed co-citations
e.g. Chronic Pain and Major Depression: Shared Psychological and Neurobiological Mechanism. - Coenzyme Q10 — 1 trial, 6 PubMed co-citations
e.g. Effects of Coenzyme Q10 on Lipid, Glycemic, and Inflammatory Markers in Metabolic Disorders: A Systematic… - Vitamin K2 — 1 trial, 6 PubMed co-citations
e.g. Vitamin K(2) (MK-7) as a novel cytoprotective agent in ovarian ischemia-reperfusion: Promoting functional… - Vitamin D — 1 trial, 6 PubMed co-citations
e.g. The Serum 25-Hydroxyvitamin D Response to Supplemental Vitamin D Is Temporarily Blunted with Elevated… - Endurance Training — 1 trial, 6 PubMed co-citations
e.g. Endurance training increases tmTNF-α and IL-6 levels in several vital organs in rats: relationship with… - Concurrent Training — 1 trial, 6 PubMed co-citations
e.g. Synergistic Effects of Microencapsulated Polyphenols and Concurrent Training on Metabolic Health and Fitness…
Commercial test availability
Interleukin-6 (IL-6), Serum — commercial laboratory test.
Links are for reference only; availability, specimen requirements and coverage vary by location.
Related Inflammatory markers in Long COVID
- Tumor Necrosis Factor-α (TNF-α) ↑
- Interleukin-1α (IL-1α) ↑
- C-Reactive Protein (CRP) ↑
- Soluble CD14 (sCD14) ↑
- Flt-1 / sVEGFR-1 ↑
- CCL4 (MIP-1β) ↑
- Cystatin D (CST5) ↑
- Pro-inflammatory cytokines (composite) ↓
Full list: Long COVID Biomarker Atlas.
Frequently asked questions
Is Interleukin-6 (IL-6) high or low in Long COVID?
Elevated. Studies summarised in the OSMF atlas report higher Interleukin-6 (IL-6) in Long COVID than in healthy controls, recovered individuals without persistent symptoms. Source: Lai et al. 2023.
What symptoms is Interleukin-6 (IL-6) associated with in Long COVID?
The cited literature associates this marker with Fatigue, systemic inflammation. These are population-level associations and do not mean the marker causes the symptoms.
Which test measures Interleukin-6 (IL-6)?
It is measured as a blood test (serum / plasma / whole blood). The standard laboratory code is LOINC 26881-5. Commercial laboratories such as Quest Diagnostics, LabCorp, Ulta Lab Tests list an orderable assay.
Is one abnormal Interleukin-6 (IL-6) result diagnostic of Long COVID?
No. No single biomarker is diagnostic of Long COVID. Interleukin-6 (IL-6) 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 Interleukin-6 (IL-6) specific to Long COVID?
No. The same marker is also reported in Gulf War Illness, Low Back Pain, Lyme Disease, ME/CFS, Major Depressive Disorder, PACVS, Rheumatoid Arthritis 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.