Important — please read first
ME/CFS is a serious, complex, and often severely disabling condition. This page describes a functional medicine investigative approach — it is not a cure, a treatment protocol, or a replacement for medical care. Many people with ME/CFS are under specialist care and should remain so. The functional testing described here works alongside that care, not instead of it. If you are severely affected, housebound, or in crisis, please speak to your GP or specialist first. Functional testing is most appropriate when someone is stable enough to engage with an investigation process.
Why "medically unexplained" is the wrong frame
For decades, ME/CFS was categorised — explicitly in clinical guidelines and implicitly in clinical practice — as a medically unexplained symptom syndrome. The implication being that the symptoms were real but the underlying biology was unknown, undetectable, or perhaps psychosomatic in origin. This framing has caused enormous harm to people who are genuinely, measurably ill.
The research picture has shifted substantially. Studies from groups including the NIH, Stanford, and University College London have identified consistent biological abnormalities across ME/CFS cohorts: impaired mitochondrial function, dysregulated HPA axis stress response, altered gut microbiome composition, persistent immune activation, elevated oxidative stress markers, and measurable differences in cellular energy metabolism. None of these findings require a new diagnostic test to detect. They are measurable with functional testing that already exists.
The problem is not that ME/CFS is biologically invisible. The problem is that the standard NHS blood test does not measure any of the systems where the dysfunction is most consistently found. A full blood count, thyroid panel, and basic metabolic screen — the workup most ME/CFS patients receive after years of investigation — are the wrong tools for the biological terrain where ME/CFS lives.
What functional testing finds in ME/CFS — consistently
Mitochondrial
Krebs cycle intermediate accumulation — succinate, fumarate, malate impairment
Metabolomix+ OAT
HPA Axis
Blunted cortisol awakening response — flat or inverted diurnal pattern
DUTCH Plus
Gut Ecology
Low microbial diversity, Clostridia overgrowth, impaired secretory IgA
GI-MAP
Immune
Persistent low-grade immune activation — elevated inflammatory markers
Blood Chemistry
Oxidative Stress
Elevated 8-OHdG — oxidative DNA damage. Low glutathione. Pyroglutamate elevated.
Metabolomix+ OAT
Neurotransmitter
Low HVA and VMA — catecholamine depletion. Low 5-HIAA — serotonin turnover reduced.
Metabolomix+ OAT
The six patterns — and what drives each one
The mitochondria are the cellular energy factories — they produce ATP through the Krebs cycle and electron transport chain. In ME/CFS, multiple research groups have documented measurable impairment at specific points in this pathway. The most consistent findings are elevated succinate (indicating Complex II / CoQ10 impairment), elevated pyruvate and lactate (indicating PDH complex impairment), and disrupted citrate cycling. The result is cells that cannot generate adequate ATP even at rest — let alone during the additional metabolic demand of physical or cognitive exertion. This is the biochemical basis of the exhaustion that doesn't respond to rest.
Succinate ↑
Fumarate ↑
Pyruvate ↑
Lactate ↑
Citrate disrupted
CoQ10 depleted
Measured by: Metabolomix+ (Organic Acids — Krebs cycle section)
The hypothalamic-pituitary-adrenal (HPA) axis governs the stress response and circadian cortisol rhythm. In ME/CFS, the consistent pattern is not high cortisol (the acute stress response) but low and flat cortisol — the cortisol awakening response (CAR) is blunted or absent, the diurnal curve is flat rather than peak-morning/trough-evening, and total daily cortisol output is reduced. This is distinct from the high-cortisol pattern of acute burnout. It represents a downstream consequence of prolonged HPA demand that has exceeded capacity — the system has downregulated its output. The practical consequence is profound morning dysfunction, inability to mount a stress response, and impaired immune surveillance (cortisol is anti-inflammatory — without it, inflammatory activity rises).
CAR blunted or flat
Low total daily cortisol
Flat diurnal curve
Low DHEA
Low cortisone
Measured by: DUTCH Plus (cortisol x4 daily + CAR + metabolites)
Multiple studies have found consistent gut microbiome abnormalities in ME/CFS cohorts — reduced bacterial diversity, increased opportunistic bacterial species, and reduced commensal species associated with short-chain fatty acid production. Clostridial overgrowth specifically is relevant: HPHPA and 4-cresol (Clostridial metabolites measurable on the Organic Acids Test) inhibit dopamine-beta-hydroxylase — the enzyme converting dopamine to noradrenaline. This is a direct mechanism by which gut dysbiosis impairs catecholamine neurotransmission and contributes to the cognitive and motivational symptoms of ME/CFS. Gut permeability (measurable via zonulin and anti-gliadin IgA on GI-MAP) allows bacterial endotoxins to cross into circulation, activating the immune system chronically and driving the systemic inflammation that characterises moderate-to-severe presentations.
Low diversity
Clostridia ↑
HPHPA ↑
4-Cresol ↑
Zonulin ↑
Secretory IgA ↓
Candida
Measured by: GI-MAP (stool) + Metabolomix+ OAT (dysbiosis markers)
ME/CFS frequently follows a viral or bacterial trigger — post-COVID ME/CFS being the most recent and most documented example, but Epstein-Barr virus, enteroviral infections, and Lyme disease have all been associated with ME/CFS onset. The immune system, having mounted an acute response to the trigger, fails to return to baseline. Persistent low-grade immune activation — elevated hsCRP, elevated inflammatory cytokines (IL-6, TNF-alpha), and evidence of ongoing immune cell dysregulation — characterises the majority of ME/CFS cases. This chronic immune activation drives systemic inflammation, depletes glutathione and antioxidant reserves, impairs mitochondrial function through oxidative stress, and maintains the HPA axis in a state of chronic demand that eventually leads to the cortisol collapse described above. The immune activation and the mitochondrial dysfunction are not separate problems — they drive each other in a self-reinforcing cycle.
hsCRP ↑
IL-6 ↑
NK cell dysfunction
Low immunoglobulins
Vitamin D ↓
Measured by: Regenerus blood chemistry (hsCRP, IL-6, immunoglobulins, vitamin D)
The combination of chronic immune activation (generating reactive oxygen species as part of the immune response) and impaired mitochondrial function (leaking electrons from the electron transport chain) creates a state of chronically elevated oxidative stress. The consequence is measurable DNA damage (elevated 8-OHdG), depleted glutathione (elevated pyroglutamic acid on the OAT), impaired antioxidant enzyme activity, and progressive damage to cellular membranes, proteins, and mitochondrial DNA. This explains one of the most clinically frustrating features of ME/CFS: the condition tends to worsen progressively without intervention rather than stabilising, because the oxidative damage accumulates and further impairs the systems that would normally mount a recovery response.
8-OHdG ↑
Pyroglutamate ↑
Low glutathione
HPLA ↑
Low CoQ10
Measured by: Metabolomix+ OAT (oxidative stress section)
The cognitive symptoms of ME/CFS — brain fog, poor concentration, word-finding difficulty, memory impairment — have a biochemical basis that is measurable on the Organic Acids Test. Low HVA (dopamine metabolite) reflects reduced dopamine turnover — driven partly by Clostridial metabolites blocking the synthesis enzyme and partly by depleted tyrosine substrate and BH4 cofactor (both methylation-dependent). Low VMA (noradrenaline metabolite) reflects catecholamine depletion across the system. Low 5-HIAA (serotonin metabolite) reflects reduced serotonin synthesis — often driven by tryptophan being diverted to the kynurenine pathway by IDO enzyme activation secondary to chronic inflammation. The kynurenine pathway elevation produces quinolinic acid — a neurotoxic NMDA agonist — which directly impairs cognitive function and worsens neurological symptoms.
HVA ↓
VMA ↓
5-HIAA ↓
Kynurenate ↑
Quinolinate ↑
HPHPA ↑
Measured by: Metabolomix+ OAT (neurotransmitter metabolites section)
Post-exertional malaise — the defining feature
Post-Exertional Malaise · PEM
Why "exercise more" is the wrong advice — and why it can make ME/CFS worse
Post-exertional malaise (PEM) — the worsening of symptoms following physical or cognitive exertion, typically delayed by 12–48 hours and lasting days to weeks — is the hallmark feature that distinguishes ME/CFS from other fatigue conditions. It has a biochemical explanation. In healthy individuals, exercise increases mitochondrial efficiency and upregulates antioxidant defences. In ME/CFS, the mitochondrial machinery is already impaired and the antioxidant reserves are already depleted. Physical or cognitive exertion generates additional oxidative stress and metabolic demand that the impaired system cannot meet or recover from in the normal timeframe. The result is a cascade of worsening: increased oxidative damage, further HPA axis suppression, immune reactivation, and extended mitochondrial dysfunction. This is why graded exercise therapy (GET) — the standard recommended intervention in older NICE guidelines — has caused documented harm in ME/CFS patients. The 2021 NICE guidelines now explicitly state that GET should not be used for ME/CFS. The functional medicine approach is pacing — staying within the energy envelope — while supporting mitochondrial function and reducing oxidative load through targeted supplementation and dietary intervention, before any increase in physical demand.
Why the five-test panel is the right investigation
No single test captures the full ME/CFS picture. The patterns described above are distributed across five different biological systems — and they interact with each other in ways that require the full picture to understand. The mitochondrial dysfunction drives the HPA axis collapse. The gut dysbiosis drives the immune activation. The immune activation drives the oxidative stress. The oxidative stress drives the mitochondrial dysfunction. These are not five separate problems. They are one interconnected dysfunctional system — and treating any one of them in isolation, without understanding the others, produces partial results at best.
Krebs cycle: Where mitochondrial function is impaired
Dysbiosis markers: HPHPA, 4-cresol, arabinose, tartaric
Neurotransmitters: HVA, VMA, 5-HIAA, kynurenate, quinolinate
Oxidative stress: 8-OHdG, pyroglutamate
Methylation: FIGLU, MMA — B-vitamin functional status
Amino acids: Tryptophan, tyrosine, glutamine, glycine
Cortisol x4 daily: Diurnal pattern and total output
CAR: Cortisol awakening response — the most sensitive HPA marker
DHEA: Adrenal reserve marker
Melatonin: Circadian rhythm and sleep architecture
OAT markers: Cross-references Metabolomix+ B-vitamin and neurotransmitter findings
Pathogens: Any persisting infectious trigger
Clostridia: Direct identification of species producing HPHPA/cresol
Candida: Confirms or rules out yeast-mediated Krebs impairment
Zonulin: Gut permeability — immune activation driver
Secretory IgA: Mucosal immune defence status
Calprotectin: Gut inflammation marker
hsCRP + IL-6: Systemic inflammatory load
Full blood count: Anaemia, immune cell patterns
Ferritin: Iron storage — often low in ME/CFS, impairs mitochondrial function
Vitamin D: Immune regulation
Thyroid: TSH, FT4, FT3 — commonly dysregulated
Homocysteine: Methylation status, cardiovascular and neurological risk
286 food antigens: Identifies dietary triggers maintaining immune activation
Milk proteins: Bos d 4/5/8 — casein reactivity drives casomorphin production relevant to brain fog
Gluten: Gliadin antibodies — zonulin driver, gut permeability maintainer
Reduces immune load: Removing reactive foods reduces total inflammatory burden
The investigation sequence — how it works in practice
The five tests are collected over a single week — one blood draw for Regenerus and HealthBeings IgG, one first-morning urine and dried blood spot for Metabolomix+, one stool sample for GI-MAP, and one four-point urine collection for DUTCH Plus. Results return over 2–3 weeks and are interpreted together in a single consultation.
1
Discovery call — is this the right approach for you right now?
Not everyone with ME/CFS is in a position to begin a functional investigation. If you are severely affected, the priority is stabilisation and specialist medical support first. The discovery call establishes whether functional testing is appropriate at this point and what reasonable expectations look like.
2
Collection — all five tests in one week
Kits are dispatched to your home address. The blood draw can be arranged through Bloods and Beyond (home phlebotomy) or a local clinic. Most ME/CFS clients prefer home collection to avoid the energy expenditure of clinic visits — this is fully supported.
3
Results consultation — the full picture, read together
All five panels are reviewed simultaneously. The patterns that emerge from reading the mitochondrial data alongside the gut dysbiosis data alongside the HPA axis data are more informative than any panel in isolation. This is where the clinical picture becomes clear and the priority hierarchy is established.
4
Protocol — sequenced, not simultaneous
The intervention is staged. The gut dysbiosis is typically addressed first — because the Clostridial and Candida metabolites are actively blocking the neurotransmitter and mitochondrial systems that everything else depends on. Antioxidant support runs in parallel. Mitochondrial cofactors are introduced once the gut burden is reduced. HPA axis support follows. The sequence matters because adding mitochondrial supplements while yeast-produced tartaric acid is actively inhibiting fumarase produces limited results.
5
Pacing — the non-negotiable throughout
Functional testing and targeted supplementation support recovery. They do not substitute for energy management. Pacing — staying consistently within the energy envelope, avoiding boom-bust cycles, and building activity tolerance only as the underlying biology improves — runs throughout the entire process. No intervention protocol works well without it.
6
Retest — confirming the shift
Selected panels are retested at 3–4 months. The OAT markers are particularly informative — mitochondrial and dysbiosis markers should show measurable improvement if the intervention is working. If they have not shifted, the protocol is reviewed. Testing removes the guesswork from "is this working?"
The most important thing I can offer someone with ME/CFS is not a protocol. It is a map of what is actually happening in their specific biochemistry — because two people with identical symptom presentations can have completely different underlying patterns, and the intervention that helps one can be ineffective or even counterproductive for the other.
What functional testing cannot do
Honesty matters here. Functional testing provides a detailed picture of the biological terrain in ME/CFS and guides targeted intervention. It does not cure ME/CFS. Recovery — where it happens — is typically slow, non-linear, and requires sustained commitment to the protocol alongside rigorous pacing. Some people see meaningful improvement over 6–12 months. Some see partial improvement over longer periods. A small proportion make full functional recovery. The variation is real and is not fully explained by the test data — individual factors including duration of illness, severity at presentation, and whether the initial trigger has resolved all affect trajectory.
What functional testing consistently does is: explain the why behind specific symptoms, identify the most important biological drivers to address, create a rational priority hierarchy for intervention, and provide objective markers of progress that are not dependent on subjective symptom reporting alone. For people who have been told their tests are normal and there is nothing to find — that explanation alone has clinical value.
On pacing and the investigation process
The collection process for five functional tests requires some energy expenditure — completing intake forms, managing kit logistics, a blood draw. For people who are severely affected, this itself needs to be paced. If you are at a point where the cognitive or physical demand of the investigation process would trigger significant PEM, it is worth discussing timing and staging with me before committing. The investigation is most useful when you are stable enough to engage with it and act on the results.
Start with a conversation
A 30-minute discovery call to discuss your history, establish whether functional testing is appropriate at this point, and set realistic expectations for what the investigation might reveal. No commitment to proceed — just clarity on whether this is the right next step for you.
Book a discovery call →
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