Summary
| Direction in ME/CFS | ↕ Inconsistent — reported as both higher and lower across studies, with no consistent direction |
|---|---|
| Category | Autonomic |
| Also described as | Sympathovagal balance |
| Compared against | HC (healthy controls) |
| Associated symptoms | Autonomic imbalance |
| Test type | Clinical or physiological test |
| Source | Nelson et al. 2019 — doi:10.1186/s12967-019-02100-4 |
| Condition atlas | ME/CFS Biomarker Atlas |
Trials, interventions and tests
In clinical-trial registrations this marker maps to the outcome term The change in LF/HF-ratio (a measure of autonomic control) during head-up tilt-test (4 registered trials use a matching outcome measure).
Clinical trials using LF/HF ratio as an outcome
- NCT06614309: Non-invasive Treatment for Long COVID (Post COVID-19 Condition) Brain Fog (Recruiting)
Outcome measure: Change in heart rate variability - NCT06170645: Transcutaneous Vagus Nerve Stimulation as a Complementary Therapy to Exercise in Chronic Fatigue (Recruiting)
Outcome measure: Ratio of Low Frequency to High Frequency (LF/HF) - NCT02924831: High-tech Acupuncture for Treatment of Chronic Fatigue Syndrome (Unknown)
Outcome measure: LF/HF - NCT01040429: The Norwegian Study of Chronic Fatigue Syndrome in Adolescents: Pathophysiology and Intervention Trial (Completed)
Outcome measure: The change in LF/HF-ratio (a measure of autonomic control) during head-up tilt-test
Interventions studied alongside this marker
Hypothesis-generating links from trial outcome usage and literature co-occurrence. Not treatment recommendations.
- Vagus nerve stimulation — 1 trial, 6 PubMed co-citations
e.g. Acute Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Autonomic Nervous System Regulation and… - Acupuncture — 1 trial, 6 PubMed co-citations
e.g. Effects of Yoga and naturopathic intervention on cardiac autonomic functions in chronic kidney disease with… - Clonidine — 1 trial, 6 PubMed co-citations
e.g. Effect of clonidine on heart rate variability during spinal anaesthesia: randomized clinical trial.
Related Autonomic markers in ME/CFS
- Heart rate variability (SDNN) ↓
- Orthostatic heart rate increment ↑
- Heart rate variability (RMSSD) ↓
- Blood pressure variability ↑
- Baroreflex sensitivity ↓
Full list: ME/CFS Biomarker Atlas.
Frequently asked questions
Is LF/HF ratio high or low in ME/CFS?
Mixed. Some studies report higher and others lower LF/HF ratio in ME/CFS compared with healthy controls, so no single direction is established. Source: Nelson et al. 2019.
What symptoms is LF/HF ratio associated with in ME/CFS?
The cited literature associates this marker with Autonomic imbalance. These are population-level associations and do not mean the marker causes the symptoms.
Which test measures LF/HF ratio?
It is measured as a clinical or physiological test. Many of the cited studies used research-grade assays, so clinical availability may vary.
Is one abnormal LF/HF ratio result diagnostic of ME/CFS?
No. No single biomarker is diagnostic of ME/CFS. LF/HF ratio 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 me-cfs.json · Browse: ME/CFS 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.