SYMPTOMS
Always Tired? 12 Blood Tests That Reveal Why
You sleep 7–8 hours. You eat well. You exercise. But you still wake up drained, hit a wall by 3pm, and can't shake the brain fog. Sound familiar? According to the NHS, around 1 in 5 people feel unusually tired at any given time, and fatigue is one of the most common reasons for a GP appointment in the UK.
The problem is that a standard NHS fatigue work-up typically covers a full blood count and thyroid-stimulating hormone (TSH) — two tests out of the twelve most commonly abnormal in people with persistent, unexplained tiredness. If those come back “in range”, you're told everything is fine. But “in range” and “optimal” are very different things.
This guide covers the 12 blood biomarkers most commonly responsible for chronic fatigue, explains why the NHS reference ranges miss subclinical problems, and describes five named result patterns that point to specific causes. It also covers the red flags that mean you should see a doctor urgently — not order a home test.
1. Why your GP says “everything's normal”
When you tell your GP you're tired, they'll typically request a full blood count (FBC) and thyroid-stimulating hormone (TSH). If haemoglobin is above 120 g/L (women) or 130 g/L (men) and TSH is between 0.4–4.5 mIU/L, you're told everything is fine. The consultation takes ten minutes, and the advice is usually “get more sleep”.
The problem is that NHS reference ranges are designed to detect disease, not to identify suboptimal function. A ferritin of 15 µg/L is “within range” but associated with fatigue in multiple studies. A TSH of 3.8 mIU/L is “normal” but sits in a zone where many people experience symptoms of subclinical hypothyroidism. A vitamin D of 30 nmol/L meets the NHS threshold for “sufficient” but is half the level associated with optimal energy and immune function in the research literature.
This is the “grey zone” — you feel terrible but you're technically not sick. A comprehensive blood panel that looks at 12 fatigue-relevant biomarkers with functional reference ranges, rather than 2–3 markers with disease-detection thresholds, is the fastest way to move from “I don't know what's wrong” to an actionable answer.
2. Fatigue vs sleepiness — why the distinction matters
Clinically, fatigue and sleepiness are not the same thing. Sleepiness means you can fall asleep easily — your eyelids droop, you nod off on the sofa, you could nap right now. That suggests a sleep disorder: obstructive sleep apnoea, poor sleep hygiene, or insufficient sleep duration.
Fatigue is different. It's a pervasive lack of energy, motivation, and mental clarity. You don't necessarily feel sleepy — you feel drained. Your muscles feel heavy. Your brain won't focus. You might sleep 9 hours and wake up feeling like you slept 4. This type of fatigue is far more likely to have a biochemical cause that shows up in blood work.
Both can coexist, and some biomarkers (particularly magnesium and ferritin) affect sleep quality as well as daytime energy. But the distinction matters because if your primary problem is excessive daytime sleepiness with loud snoring and a neck circumference above 43cm (men) or 40cm (women), the right investigation is a sleep study, not a blood test. The NICE guideline NG202 on sleep apnoea covers referral criteria.
3. The 12 biomarkers behind persistent tiredness
These are the markers most commonly abnormal in adults presenting with unexplained fatigue, drawn from NICE clinical guidelines, the BMJ, and peer-reviewed literature on chronic fatigue investigation. No single marker explains every case — the power is in testing all twelve simultaneously and reading the pattern.
1. Ferritin (iron stores)
Ferritin measures your body's stored iron. Iron is essential for haemoglobin, which carries oxygen to every cell. When ferritin drops, oxygen delivery falls — and fatigue is the first symptom, months before haemoglobin itself becomes abnormal. The NHS lower limit is 12–15 µg/L, but a 2012 study in the Canadian Medical Association Journal found that women with unexplained fatigue and ferritin below 50 µg/L showed significant improvement when supplemented with iron. The threshold for symptomatic benefit is roughly 50–100 µg/L — three to six times higher than the NHS lower limit.
2. TSH (thyroid-stimulating hormone)
TSH is the pituitary hormone that tells your thyroid to produce energy-regulating hormones. When the thyroid underperforms, TSH rises. The NHS reference range extends to 4.5–5.0 mIU/L, but the Endocrine Society and multiple population studies suggest that TSH above 2.5 mIU/L may indicate early thyroid dysfunction, particularly if free T4 sits in the lower third of its range. This is subclinical hypothyroidism — the most commonly missed thyroid cause of fatigue.
3. Free T4 & Free T3
TSH tells you the brain's demand signal. Free T4 and free T3 tell you what the thyroid is actually producing. T4 is the storage hormone; T3 is the active form that drives cellular metabolism. Some people have a normal TSH but poor T4‑to‑T3 conversion, meaning their cells are energy-starved despite “normal” TSH. This pattern is invisible without testing all three. GPs rarely request free T3 — it's one of the biggest gaps in standard NHS thyroid assessment.
4. Vitamin D
Vitamin D receptors exist in virtually every cell, and low levels impair mitochondrial function — your cellular energy factories. In the UK, SACN estimates that 1 in 5 adults are deficient year-round, rising to nearly half during winter. The NHS considers 25 nmol/L “sufficient”, but the Endocrine Society Clinical Practice Guideline recommends maintaining levels above 75 nmol/L, and research links levels of 100–150 nmol/L with optimal energy, mood, and immune function.
5. Vitamin B12
B12 is critical for red blood cell formation and nerve function. Deficiency causes megaloblastic anaemia — oversized red blood cells that can't carry oxygen efficiently — and directly impairs neurological function, causing brain fog, poor concentration, and fatigue. Serum B12 below 200 pg/mL is deficient, but symptoms often appear below 400–500 pg/mL, well within the NHS “normal” range. Vegans, vegetarians, adults over 50, and anyone on proton pump inhibitors (PPIs) are at elevated risk.
6. Folate (vitamin B9)
Folate works alongside B12 in red blood cell production and DNA synthesis. Deficiency causes the same megaloblastic anaemia as B12 deficiency. Serum folate below 7 nmol/L is deficient; optimal is 20–45 nmol/L. If you carry the MTHFR gene variant (which affects roughly 40% of the population), you may process dietary folate less efficiently and need supplementation with the active form, methylfolate.
7. HbA1c (blood sugar control)
HbA1c measures your average blood sugar over 2–3 months. Impaired blood sugar regulation — insulin resistance or pre-diabetes — causes energy crashes, post-meal sleepiness, and the classic “3pm wall”. An estimated 13.6 million people in England are at risk of type 2 diabetes, and most don't know it. HbA1c of 42–47 mmol/mol indicates pre-diabetes, but even values at the upper end of “normal” (38–41) can cause energy fluctuations.
8. Testosterone
Testosterone is not just a sex hormone. It regulates energy, motivation, muscle recovery, and cognitive clarity in both men and women. In men, total testosterone below 12 nmol/L is the BSSM threshold for investigation, but fatigue symptoms commonly appear at levels below 15 nmol/L, especially in combination with low free testosterone or elevated SHBG. In women, low testosterone contributes to fatigue, low motivation, and reduced exercise tolerance — yet it is almost never tested by GPs outside fertility clinics.
9. Cortisol
Cortisol follows a diurnal rhythm: it should peak within 30–60 minutes of waking (the cortisol awakening response) and decline through the afternoon and evening. Chronic stress can disrupt this rhythm — either blunting the morning peak (resulting in difficulty waking and morning exhaustion) or keeping levels elevated into the evening (causing wired-but-tired insomnia). A single fasting morning cortisol gives a snapshot of where you sit on this curve. Values below 250 nmol/L at 9am warrant further investigation; values above 600 nmol/L suggest a stress-driven pattern.
10. Magnesium
Magnesium is involved in over 300 enzymatic reactions, including ATP (energy) production. It is also critical for sleep quality — and poor sleep is one of the most obvious causes of daytime fatigue. Modern diets are lower in magnesium than historical diets, and stress depletes it rapidly. Serum magnesium is a poor marker (only 1% of body magnesium is in the blood), but levels below 0.85 mmol/L strongly suggest deficiency, and even “normal” levels do not rule it out.
11. hs-CRP (high-sensitivity C-reactive protein)
Chronic low-grade inflammation is an underappreciated driver of fatigue. When your immune system is constantly activated — by visceral fat, gut dysfunction, chronic stress, or poor diet — it produces inflammatory cytokines that directly cause tiredness, muscle aches, and brain fog. This is the same mechanism that makes you feel exhausted when you have the flu. hs-CRP below 1.0 mg/L is ideal; between 1.0–3.0 suggests moderate inflammation; above 3.0 indicates significant inflammation.
12. Full blood count (FBC)
The full blood count is the one test your GP almost always runs — and for good reason. It reveals anaemia (low haemoglobin), infection markers (elevated white cells), and red cell size (MCV), which distinguishes iron-deficiency anaemia (small cells) from B12/folate-deficiency anaemia (large cells). It is essential — but it is a starting point, not an endpoint.
4. NHS reference ranges vs optimal ranges
The table below shows why “normal” does not mean “optimal”. NHS ranges are designed to catch disease. Functional/optimal ranges reflect the levels where research shows most people feel and perform their best. The grey zone between the two is where millions of people live with fatigue.
| Biomarker | NHS “normal” | Optimal / functional | Grey zone |
|---|---|---|---|
| Ferritin | 12–300 µg/L | 50–150 µg/L | 12–50 — “normal” but symptomatic |
| TSH | 0.4–4.5 mIU/L | 0.5–2.5 mIU/L | 2.5–4.5 — subclinical hypothyroidism zone |
| Free T4 | 9–25 pmol/L | 15–20 pmol/L | 9–14 — lower third of range |
| Vitamin D | >25 nmol/L | 75–150 nmol/L | 25–75 — “sufficient” but suboptimal |
| Vitamin B12 | 200–900 pg/mL | 400–900 pg/mL | 200–400 — symptoms common despite “normal” |
| Folate | >7 nmol/L | 20–45 nmol/L | 7–20 — low normal, especially with MTHFR |
| HbA1c | <42 mmol/mol | <36 mmol/mol | 36–41 — energy crashes, pre-pre-diabetes |
| Testosterone (men) | 8.6–29 nmol/L | 15–25 nmol/L | 8.6–15 — “normal” but low-energy symptoms |
| Cortisol (9am) | 170–700 nmol/L | 350–550 nmol/L | <250 — blunted awakening response |
| Magnesium | 0.7–1.0 mmol/L | 0.85–0.95 mmol/L | 0.7–0.85 — functional depletion |
| hs-CRP | <5.0 mg/L | <1.0 mg/L | 1.0–3.0 — chronic low-grade inflammation |
| Haemoglobin (men) | 130–170 g/L | 140–160 g/L | 130–140 — borderline low, fatigue common |
Sources: NICE NG24 (blood transfusion thresholds), NICE NG145 (thyroid disease), SACN (vitamin D), BSSM 2022 (testosterone). Optimal/functional ranges reflect consensus from the cited clinical literature, not a single source.
5. Five named fatigue patterns — and what each one means
Most people with persistent fatigue don't have a single abnormal marker. They have a pattern — a combination of suboptimal values that interact to drain energy. Here are the five patterns we see most commonly.
Pattern 1: The depleted absorber
Signature: low ferritin + low B12 + low folate ± low vitamin D
Multiple nutrient deficiencies simultaneously suggest an absorption problem rather than a dietary gap. Common causes include undiagnosed coeliac disease (affects 1 in 100 in the UK, but NICE NG20 estimates 76% are undiagnosed), long-term PPI use suppressing stomach acid, or inflammatory bowel disease. If you see this pattern, a tTG-IgA coeliac screen is the next step.
Pattern 2: The subclinical thyroid
Signature: TSH 2.5–4.5 + free T4 in lower third + normal or low free T3
Everything is technically “in range” but the thyroid is working harder than it should (elevated TSH) and producing less active hormone than optimal (low-normal T4 and T3). This person feels cold, sluggish, gains weight easily, and sleeps 9 hours but never feels rested. GPs will typically say “thyroid is fine” because TSH is under 4.5. A full thyroid panel including FT3 reveals what TSH alone misses.
Pattern 3: The hormonal energy crash
Signature: low testosterone + blunted morning cortisol ± low vitamin D
This pattern is most common in men over 35 and perimenopausal women. Testosterone drives motivation, muscle recovery, and mental drive. When it falls alongside a blunted cortisol awakening response, the result is profound morning fatigue, difficulty starting the day, loss of motivation for exercise, and a general sense of “I just can't be bothered”. This is frequently misdiagnosed as depression. See our low testosterone guide for more.
Pattern 4: The metabolic staller
Signature: HbA1c 38–42 + elevated hs-CRP + low magnesium
Blood sugar regulation is impaired but not yet diabetic. The body is producing more insulin than it should to keep glucose under control, and the metabolic stress drives chronic low-grade inflammation. Magnesium depletion (common in insulin resistance) worsens both sleep and energy. This person has energy crashes after meals, craves carbohydrates, and gains weight around the midsection. Our metabolic health guide covers the insulin resistance pathway in detail.
Pattern 5: The chronic inflammation drain
Signature: hs-CRP 1.5–5.0 + low ferritin + variable thyroid
Persistent low-grade inflammation hijacks iron metabolism (a process called “anaemia of chronic disease” or functional iron deficiency). The body sequesters iron away from the bloodstream as an immune defence, so ferritin can appear normal or even elevated while the body is functionally iron-starved. This pattern is common in autoimmune conditions, chronic gut inflammation, obesity, and chronic stress states. It requires both hs-CRP and ferritin to interpret correctly — neither alone tells the full story.
6. Thyroid deep-dive: why TSH alone isn't enough
The thyroid controls your basal metabolic rate — literally how fast every cell in your body produces energy. When it underperforms, everything slows: energy, metabolism, cognition, mood, recovery. Subclinical hypothyroidism is the most common thyroid presentation in fatigue, affecting an estimated 4–10% of UK adults (NICE NG145).
The standard GP test is TSH only. If TSH is under 4.5, the thyroid is considered “normal”. The problem is that TSH is a pituitary hormone, not a thyroid hormone. It measures demand, not supply. Testing TSH alone is like looking at how hard someone is pressing the accelerator without checking whether the car is actually moving.
A complete thyroid assessment requires three markers:
- TSH — how hard the pituitary is shouting at the thyroid
- Free T4 — how much storage hormone the thyroid is producing
- Free T3 — how much active hormone reaches the cells
The conversion of T4 to T3 happens primarily in the liver and kidneys and depends on selenium, zinc, and adequate cortisol. Chronic stress, nutrient deficiencies, and liver dysfunction can all impair this conversion — meaning the thyroid is working fine but the active hormone never reaches your cells. This pattern (normal TSH, normal T4, low T3) is invisible without testing all three.
7. Hormonal fatigue: the overlooked cause
Testosterone and cortisol are rarely included in a standard GP fatigue work-up, yet they are among the most common causes of persistent tiredness in adults aged 30–55.
In men
Male testosterone declines by approximately 1–2% per year after age 30. By age 45, a significant proportion of men have total testosterone below the functional threshold of 15 nmol/L. Symptoms include fatigue, reduced motivation, difficulty recovering from exercise, increased body fat, irritability, and low libido. This cluster is frequently misdiagnosed as depression or attributed to “getting older”. The BSSM 2022 guidelines recommend investigating testosterone when fatigue symptoms are present alongside other androgen-deficiency symptoms.
In women
Women produce testosterone too — in smaller quantities, primarily from the ovaries and adrenal glands. During perimenopause (typically ages 40–55), both oestrogen and testosterone decline, causing fatigue, brain fog, reduced exercise tolerance, and mood changes that overlap heavily with the symptoms of depression and hypothyroidism. Our perimenopause blood test guide covers the hormonal shifts in detail.
Cortisol and the stress–fatigue cycle
Chronic psychological stress doesn't just make you feel tired — it physically reshapes your cortisol rhythm. Initially, cortisol rises (the “wired and tired” phase). Over time, the HPA axis can become blunted, producing a flat cortisol curve with poor morning output. This results in profound morning fatigue, difficulty waking, and a paradoxical inability to sleep at night. While “adrenal fatigue” is not a recognised medical diagnosis, HPA axis dysregulation is well-documented — see our adrenal fatigue guide for the evidence.
8. Blood sugar and fatigue: the 3pm crash
If your fatigue follows a predictable pattern — energy crash 1–2 hours after meals, worst in the early afternoon, temporarily relieved by sugar or caffeine — the cause is almost certainly impaired blood sugar regulation.
Insulin resistance means your cells respond poorly to insulin, so the pancreas produces more to compensate. This over-production drives reactive hypoglycaemia after meals: blood sugar spikes, then crashes below baseline, triggering fatigue, brain fog, irritability, and sugar cravings. Over time, HbA1c creeps up as average glucose rises. The NICE NG28 guideline on type 2 diabetes prevention recommends early identification through HbA1c screening in at-risk populations.
Adding fasting insulin to HbA1c provides an even earlier signal: insulin can be elevated for years before HbA1c starts to rise, making it the earliest detectable marker of metabolic dysfunction. Our pre-diabetes guide covers the progression from insulin resistance to diabetes and what to do at each stage.
9. Red flags — when tiredness needs urgent investigation
Most persistent fatigue has a benign, treatable cause. But certain combinations of symptoms require urgent medical assessment, not a home blood test. See your GP or attend A&E if fatigue is accompanied by any of the following:
SEEK URGENT MEDICAL ADVICE
- Unexplained weight loss — loss of more than 5% of body weight over 3–6 months without dietary changes. NICE refers to this as a potential cancer indicator (NG12).
- Night sweats drenching bedsheets — especially with enlarged lymph nodes. This is a “B symptom” associated with lymphoma and requires urgent investigation.
- New lump or lymph node swelling persisting more than 2 weeks.
- Fatigue with persistent fever — fever lasting more than 2 weeks without obvious infection requires investigation for malignancy, autoimmune disease, or endocarditis.
- Severe breathlessness on minimal exertion, new-onset — may indicate severe anaemia (Hb <80 g/L), cardiac failure, or pulmonary embolism.
- Jaundice (yellowing of skin or eyes) — suggests liver failure or haemolytic anaemia and needs same-day assessment.
- Fatigue following a recent infection that is worsening, not improving, after 4 weeks — may indicate post-viral fatigue or developing ME/CFS, which benefits from early pacing strategies.
- New onset in adults over 60 with no obvious cause — cancer risk rises with age; a wider investigation (CT, tumour markers) may be appropriate.
If none of these apply and your fatigue has persisted for more than 4 weeks, a comprehensive blood panel is the logical next step. Most causes of persistent fatigue are nutritional, hormonal, or metabolic — and all are detectable in blood.
10. Evidence-based management by biomarker
If your blood results show one or more suboptimal markers, here is what the evidence says about addressing each one. Always retest at 8–12 weeks to confirm improvement.
| Biomarker | First-line action | Retest |
|---|---|---|
| Low ferritin | Iron bisglycinate 20–25 mg/day with vitamin C; take away from tea/coffee/dairy | 12 weeks |
| Elevated TSH / low FT4 | GP referral if TSH >4.5; selenium 200 µg/day supports T4→T3 conversion; ensure iodine adequacy | 6–8 weeks |
| Low vitamin D | Vitamin D3 2,000–4,000 IU/day maintenance; up to 10,000 IU/day for 8–12 weeks if <30 nmol/L (under supervision); take with fat | 12 weeks |
| Low B12 | Methylcobalamin 1,000 µg sublingual daily; if <200 pg/mL, GP for loading injections | 8 weeks |
| Low folate | Methylfolate (5-MTHF) 400–800 µg/day; dark leafy greens, legumes | 8 weeks |
| Elevated HbA1c | Reduce refined carbohydrates; increase protein + fibre at meals; 150 min/week moderate exercise; GP if ≥42 | 12 weeks |
| Low testosterone | Optimise sleep, resistance training, vitamin D, zinc; GP referral if <12 nmol/L (men) for TRT assessment | 8–12 weeks |
| Blunted cortisol | Structured stress management; ashwagandha 600 mg/day (KSM-66); ensure adequate sleep; GP if <170 nmol/L | 8 weeks |
| Low magnesium | Magnesium glycinate or threonate 300–400 mg elemental in the evening; avoid oxide (poor absorption) | 4–6 weeks |
| Elevated hs-CRP | Omega-3 (2–4 g EPA+DHA/day); address root cause (visceral fat, gut health, sleep, stress) | 12 weeks |
11. GP fatigue panel vs Helvy — what you actually get tested
This is what a typical NHS fatigue investigation covers compared to a Helvy comprehensive panel.
| Biomarker | NHS GP | Helvy Essential | Helvy Performance |
|---|---|---|---|
| Full blood count | Yes | Yes | Yes |
| TSH | Yes | Yes | Yes |
| Free T4 | Sometimes | Yes | Yes |
| Free T3 | Rarely | — | Yes |
| Ferritin | Sometimes | Yes | Yes |
| Vitamin D | Rarely | Yes | Yes |
| Vitamin B12 | Sometimes | Yes | Yes |
| Folate | Sometimes | Yes | Yes |
| HbA1c | Rarely | Yes | Yes |
| Testosterone | Rarely | — | Yes |
| Cortisol | Rarely | — | Yes |
| Magnesium | Rarely | Yes | Yes |
| hs-CRP | Rarely | Yes | Yes |
A typical NHS fatigue investigation covers 2–4 of these markers. The Helvy Essential panel covers 10, and the Performance panel covers all 13 — including the hormonal markers (testosterone, cortisol, free T3) that GPs almost never request for a fatigue presentation.
12. Which Helvy panel should you choose?
If fatigue is your primary concern:
- Essential (£129) — covers the nutritional and metabolic markers (ferritin, vitamin D, B12, folate, HbA1c, magnesium, hs-CRP, TSH, FT4, FBC). Ideal first test if you've never had a comprehensive panel.
- Performance (£199) — adds testosterone, cortisol, and free T3. Recommended if you suspect hormonal causes (age 35+, exercise recovery declining, low motivation, libido changes) or if you want the most complete picture.
Both include a doctor-reviewed results report with personalised recommendations, delivered within 5 working days of your sample reaching the lab. If any result requires GP follow-up, we flag it clearly with a recommended action.
13. Frequently asked questions
Can a blood test really tell me why I'm tired?
Yes. In the majority of cases, persistent unexplained fatigue has a measurable biochemical cause — most commonly iron depletion, thyroid dysfunction, vitamin D deficiency, or hormonal imbalance. A comprehensive blood panel testing 10–13 markers simultaneously is the most efficient way to identify or rule out these causes.
What blood tests should I ask my GP for if I'm always tired?
At minimum: full blood count, ferritin, TSH with free T4, vitamin D, vitamin B12, folate, and HbA1c. GPs can request all of these on the NHS, though availability varies by Clinical Commissioning Group. If your GP only offers FBC and TSH, you can request the additional markers or order a comprehensive private panel.
My blood tests came back normal but I'm still exhausted. What now?
“Normal” means within the NHS reference range, which is designed to detect disease rather than identify suboptimal function. Check your actual values against the optimal ranges in the table above — many people with “normal” results have ferritin, vitamin D, or thyroid markers in the grey zone where fatigue symptoms are common. If your values are genuinely optimal and fatigue persists, consider sleep disorders, chronic fatigue syndrome (ME/CFS), or mental health causes.
How quickly will I feel better after addressing a deficiency?
It depends on the marker. Iron supplementation typically takes 8–12 weeks to restore ferritin levels. Vitamin D can take 6–12 weeks of supplementation. Thyroid medication (levothyroxine) usually shows improvement within 4–6 weeks. B12 injections often produce noticeable improvement within days. In general, expect 4–12 weeks for full resolution.
Can tiredness be a sign of something serious?
Rarely, but yes. Fatigue with unexplained weight loss, night sweats, persistent fever, or new lumps requires urgent GP assessment to rule out malignancy or serious systemic disease. See the red flags section above. In the vast majority of cases, persistent fatigue has a benign, treatable cause.
Is a finger-prick blood test accurate enough for these markers?
Yes. All Helvy tests are processed by UKAS-accredited NHS laboratories using the same equipment and quality standards as hospital samples. Finger-prick (capillary) blood collection has been validated against venous blood draws for all the markers in this guide, with clinically equivalent accuracy.
Should I fast before a fatigue blood test?
A 10–12 hour overnight fast is recommended if your panel includes HbA1c or fasting insulin, as food intake affects glucose-related markers. For other markers (ferritin, thyroid, vitamin D, B12), fasting is not strictly necessary but may reduce variability. Our fasting blood test guide covers the details.
14. The bottom line
Persistent tiredness is not normal. It is not “just stress” and it is not “just getting older”. In most cases, there is a measurable biological explanation — and it is fixable once you know what it is.
A standard GP fatigue work-up checks 2–4 markers. A comprehensive panel checking all 12 fatigue-relevant biomarkers, interpreted against functional reference ranges rather than disease-detection thresholds, is the fastest route from “I don't know what's wrong” to an actionable plan.
Stop guessing. Test the 12 markers that actually explain fatigue. See the pattern. Fix the cause.
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Medical disclaimer: This content is for informational purposes only and does not constitute medical advice. Persistent fatigue can have many causes including sleep disorders, mental health conditions, ME/CFS, and chronic diseases. If you are experiencing severe or worsening fatigue, particularly with any of the red flag symptoms described above, please consult your GP. All Helvy blood tests are processed by UKAS-accredited NHS laboratories and reviewed by a GMC-registered doctor.
Last updated: April 2026 · By Helvy · Medically reviewed