Summary
| Direction in Gulf War Illness | ↕ Inconsistent — reported as both higher and lower across studies, with no consistent direction |
|---|---|
| Category | Neurological |
| Also described as | HPA axis hormone |
| Compared against | HGV (healthy Gulf War veteran controls) |
| Associated symptoms | Fatigue, stress response |
| Test type | Blood test (serum / plasma / whole blood) |
| LOINC code | 2143-6 |
| Source | Gean et al. 2021 — doi:10.1016/j.lfs.2021.119456 |
| Condition atlas | Gulf War Illness Biomarker Atlas |
Other conditions where Cortisol is reported
- Cortisol in Long COVID — ↕ inconsistent vs HC
- Cortisol in Major Depressive Disorder — ↑ elevated vs MDD patients vs healthy controls (HPA axis dysregulation)
- Cortisol (diurnal rhythm) in ME/CFS — ↕ inconsistent vs HC
See the cross-condition hub: Cortisol across conditions.
Trials, interventions and tests
In clinical-trial registrations this marker maps to the outcome term Cortisol Level (17 registered trials use a matching outcome measure).
Clinical trials using Cortisol (diurnal) as an outcome
- NCT06928480: Effectiveness and Acceptability of the Unified Protocol for the Transdiagnostic Treatment of Emotional Disorders in People With Long COVID-19. (Recruiting)
Outcome measure: Cortisol and cortisona levels - NCT05795816: Effectiveness of Testofen Compared to Placebo on Long COVID Symptoms (Completed)
Outcome measure: Change in Pathology results via Blood test - NCT05630040: VNS for Long-COVID-19 (Completed)
Outcome measure: Morning salivary cortisol levels - NCT06456502: Effectiveness of Non-invasive Neuromodulation in Patients With Long-COVID (Recruiting)
Outcome measure: Cortisol and alpha amylase levels - NCT05556733: FMT for Post-acute COVID-19 Syndrome (Unknown)
Outcome measure: Change in blood cortisol - NCT06042777: Non-pharmacological and TCM-based Treatment for Long COVID Symptoms (Unknown)
Outcome measure: Neurobiological outcomes - NCT05918965: Vagus Stimulation in Female Long COVID Patients. (Unknown)
Outcome measure: Saliva cortisol - NCT05681455: Physiotherapy for Persistent Function by Superficial Neuromodulation (Unknown)
Outcome measure: Cortisol levels
9 more trials reference this marker.
Interventions studied alongside this marker
Hypothesis-generating links from trial outcome usage and literature co-occurrence. Not treatment recommendations.
- Acupuncture — 2 trials, 6 PubMed co-citations
e.g. Role of gamma-aminobutyric acid-ergic neurons in the thalamic reticular nucleus in regulating sleep-wake… - Vagus nerve stimulation — 1 trial, 6 PubMed co-citations
e.g. Stress, inflammation, and resilience among patients with oral squamous cell carcinoma undergoing multimodal… - Exercise therapy — 1 trial, 6 PubMed co-citations
e.g. Dance Movement Therapy Reduces Stress-Related Physiological Markers and Improves Life Satisfaction in Adults. - Mental Training — 1 trial, 6 PubMed co-citations
e.g. How mindfulness-based training improves stress-related health: a selective review of randomized clinical… - Anakinra — 1 trial, 6 PubMed co-citations
e.g. Evaluation of the Effect of IL-1 Antagonists on Pituitary Function.
Commercial test availability
Cortisol — commercial laboratory test.
Links are for reference only; availability, specimen requirements and coverage vary by location.
Related Neurological markers in Gulf War Illness
Full list: Gulf War Illness Biomarker Atlas.
Frequently asked questions
Is Cortisol (diurnal) high or low in Gulf War Illness?
Mixed. Some studies report higher and others lower Cortisol (diurnal) in Gulf War Illness compared with healthy Gulf War veteran controls, so no single direction is established. Source: Gean et al. 2021.
What symptoms is Cortisol (diurnal) associated with in Gulf War Illness?
The cited literature associates this marker with Fatigue, stress response. These are population-level associations and do not mean the marker causes the symptoms.
Which test measures Cortisol (diurnal)?
It is measured as a blood test (serum / plasma / whole blood). The standard laboratory code is LOINC 2143-6. Commercial laboratories such as Quest Diagnostics, LabCorp, Ulta Lab Tests list an orderable assay.
Is one abnormal Cortisol (diurnal) result diagnostic of Gulf War Illness?
No. No single biomarker is diagnostic of Gulf War Illness. Cortisol (diurnal) 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 Cortisol (diurnal) specific to Gulf War Illness?
No. The same marker is also reported in Long COVID, ME/CFS, Major Depressive Disorder 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 gulf-war-illness.json · Browse: Gulf War Illness 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.