BRAIN HEALTH
Can a Blood Test Detect Dementia Early? What Science Says in 2026
Dementia affects roughly 944,000 people in the UK, and that number is projected to exceed 1.6 million by 2050. For decades, diagnosing Alzheimer's disease — the most common cause — required expensive brain scans or invasive lumbar punctures. Only about 2% of people diagnosed with Alzheimer's in the UK currently access these gold-standard tests.
That is starting to change. A new generation of blood biomarkers — particularly one called p-tau217 — can detect the earliest signs of Alzheimer's pathology with accuracy approaching that of a PET scan. The NHS is already trialling it. This guide explains where the science stands, what you can test today for brain health, and what to watch for next.
1. Can a Blood Test Detect Dementia?
Not yet — but very soon. Experimental blood tests can now detect the protein signatures of Alzheimer's disease years before symptoms appear. The most promising marker, p-tau217, performs comparably to PET brain scans in identifying amyloid and tau pathology. A February 2026 study in Nature Medicine showed that p-tau217 “clocks” can predict when Alzheimer's symptoms will appear — potentially decades in advance.
However, these tests are not yet available to consumers in the UK. They are in clinical trials within the NHS, with a target of routine clinical use by 2029. In the meantime, several standard blood biomarkers have strong evidence linking them to long-term brain health — and these are available to test today.
2. Which Blood Biomarkers Are Being Researched for Dementia?
Five blood biomarkers are at the forefront of Alzheimer's research. Each reflects a different aspect of what goes wrong in the brain:
| Biomarker | What it measures | Strength |
|---|---|---|
| p-tau217 | Phosphorylated tau protein — reflects both amyloid and tau buildup | Most accurate single blood marker; rivals PET scans |
| p-tau181 | Earlier-generation tau marker | Good predictive value (AUC 70–83%); less specific than p-tau217 |
| GFAP | Glial fibrillary acidic protein — astrocyte activation and neuroinflammation | Tracks amyloid-driven tau progression across brain regions |
| NfL | Neurofilament light chain — general neuronal damage | Sensitive to neurodegeneration but not Alzheimer's-specific |
| Aβ42/40 ratio | Amyloid-beta peptide ratio — reflects brain amyloid plaque burden | Weaker standalone performance; best combined with p-tau217 |
Research published in Alzheimer's & Dementia confirms that the combination of p-tau217, GFAP and NfL provides the most comprehensive blood-based picture of Alzheimer's pathology currently possible.
3. p-tau217: The Most Promising Dementia Blood Test
p-tau217 (phosphorylated tau at threonine 217) is widely considered the single most accurate blood biomarker for Alzheimer's disease. It reflects both amyloid plaque accumulation and tau tangle formation — the two hallmark pathologies of Alzheimer's.
A landmark February 2026 study from Washington University, published in Nature Medicine, studied 603 participants and found that p-tau217 levels can be used to build “Alzheimer's clocks” — models that predict when a person will develop symptoms. The key finding: a person whose p-tau217 begins rising at age 60 may not develop symptoms for roughly 20 years; at age 80, the window narrows to about 11 years.
This matters because it opens a window for intervention. If future anti-amyloid therapies (such as lecanemab and donanemab, already approved in some countries) prove effective at slowing progression, catching the disease early through a simple blood test could fundamentally change outcomes.
For now, p-tau217 is established in only one NHS clinical laboratory — the National Hospital for Neurology and Neurosurgery — and only for research purposes. It is not yet available as a consumer test in the UK.
4. The NHS ADAPT Trial: When Will Blood Tests Be Available?
The most significant UK development is the ADAPT trial (Alzheimer's Disease Diagnosis And Plasma p-Tau217), led by Professor Jonathan Schott and Dr Ashvini Keshavan at University College London.
ADAPT TRIAL AT A GLANCE
- Launched:August 2025, Essex Partnership University NHS Foundation Trust
- Scale:1,100 participants across 20 NHS memory service centres
- Design:Half receive p-tau217 results within 3 months; half after 12 months
- Funding:Blood Biomarker Challenge — Alzheimer's Research UK, Alzheimer's Society, People's Postcode Lottery
- Goal:Routine NHS blood test for Alzheimer's diagnosis by 2029
Professor Schott has stated: “We now have a blood test for Alzheimer's disease backed by strong scientific evidence.” The trial will measure whether providing early blood-test results speeds up diagnosis compared with the current pathway, which typically takes 12–18 months from first GP appointment to specialist confirmation.
Additional UK trials are running at the Warneford Hospital in Oxford and at centres across England, Scotland and Wales. The University of Cambridge has described these as the “first UK-wide trials on blood tests for diagnosing dementia”.
5. What About the Galleri Cancer Blood Test?
You may have seen news about a “blood test on the NHS that detects disease early.” That is most likely the Galleri test by GRAIL — and it screens for cancer, not dementia. The two are entirely separate.
Galleri detects abnormal cell-free DNA fragments shed by tumours and can screen for signals from roughly 50 cancer types. The NHS-Galleri trial enrolled over 140,000 participants aged 50–77. February 2026 results were mixed: the test did not meet its primary endpoint but did detect cancers at four times the rate of standard care and substantially reduced late-stage diagnoses.
Galleri is not available outside clinical trials in the UK. Cancer Research UK does not yet recommend it for general screening. We mention it here only because the two tests are often confused in news coverage.
6. What You Can't Get Yet — and What You Can
To be direct: you cannot buy a dementia blood test in the UK today. p-tau217 is in clinical trials. In the US, Quest Diagnostics began offering p-tau217 testing in April 2024, but it is not available to UK consumers and is not a standalone diagnostic tool — it must be interpreted alongside clinical assessment.
What you can do today is check the standard blood biomarkers that have strong, independent evidence linking them to long-term brain health and dementia risk. These are markers that any comprehensive blood panel already includes — and unlike p-tau217, they are modifiable. If your levels are off, you can take action now.
7. Six Blood Biomarkers Linked to Brain Health You Can Check Today
None of these markers diagnose dementia. But the research is clear that keeping them in optimal range is one of the most evidence-based things you can do to protect your brain long-term.
01HbA1c (Blood Sugar Control)
Type 2 diabetes roughly doubles the risk of developing dementia. A 2025 meta-analysis in Diabetic Medicine covering over seven million individuals found a dose-response relationship: HbA1c of 8–9% was associated with 15% higher dementia risk, 9–10% with 26% higher risk, and above 10% with 40% higher risk (relative to HbA1c 6–7%).
Even HbA1c variability — blood sugar that swings up and down over time — independently increases dementia hazard. Keeping HbA1c stable and below 42 mmol/mol (6.0%) is the optimal target for brain health, regardless of whether you have a diabetes diagnosis.
02Homocysteine & B Vitamins
Elevated homocysteine is one of the strongest modifiable risk factors for both vascular dementia and Alzheimer's disease. A landmark study published in the New England Journal of Medicine established the association, and subsequent intervention trials showed that B vitamin supplementation (B6, B12, folate) lowered homocysteine by 30% and slowed brain atrophy by up to 53% in those with the highest baseline levels.
An International Consensus Statement confirmed elevated homocysteine as a modifiable risk factor for cognitive decline. Optimal levels are below 10 µmol/L. Testing homocysteine is particularly important because it is one of the few dementia risk factors where treatment (B vitamins) has been shown to slow brain shrinkage in randomised controlled trials.
03Vitamin D
Vitamin D deficiency is associated with a substantially increased risk of all-cause dementia and Alzheimer's disease. A 2025 meta-analysis in Frontiers in Neurology found a 1.2% reduction in dementia risk for every 10 nmol/L increase in serum vitamin D.
The mechanisms are well-characterised: vitamin D reduces amyloid deposition, tau phosphorylation, oxidative stress and neuroinflammation. A large UK Biobank prospective study confirmed the association in a British population. Given that roughly a quarter of UK adults are vitamin D deficient, this is one of the most actionable findings in dementia prevention.
Read our vitamin D biomarker guide → | Vitamin D deficiency UK guide →
04hs-CRP (Systemic Inflammation)
Chronic low-grade inflammation is increasingly recognised as a driver of neurodegeneration. A study in JAMA Neurology found that elevated midlife CRP is associated with increased Alzheimer's risk — particularly in carriers of the APOE ε4 gene variant, the strongest genetic risk factor for late-onset Alzheimer's.
Optimal hs-CRP for brain health is below 1.0 mg/L. Levels above 3.0 mg/L represent significantly elevated risk. Unlike genetic factors, inflammation is modifiable through diet, exercise, sleep quality and stress management.
05Thyroid Function (TSH)
The American Neurologic Association recommends thyroid function testing as part of the routine dementia workup. The relationship is U-shaped: both abnormally low and abnormally high TSH are associated with increased Alzheimer's risk. Subclinical hyperthyroidism (suppressed TSH with normal fT4) carries a particularly elevated risk.
A dose-response meta-analysis confirmed the association across multiple large cohorts. Thyroid dysfunction is treatable, making it one of the most important reversible contributors to cognitive decline.
Read our thyroid (TSH) biomarker guide → | Thyroid blood test UK guide →
06Vitamin B12
B12 deficiency is associated with hippocampal atrophy on MRI — shrinkage of the brain region most critical for memory formation. A 2025 study in the Journal of Cerebral Blood Flow & Metabolism confirmed the link between low B12 and accelerated cognitive decline.
B12 deficiency is common in the UK, particularly among vegetarians, vegans, adults over 60, and people taking metformin or proton pump inhibitors. Because B12 also contributes to homocysteine metabolism, deficiency creates a double risk — directly through neuronal damage and indirectly through elevated homocysteine.
Brain Health Biomarkers: Quick Reference
| Marker | Optimal for brain health | Modifiable? |
|---|---|---|
| HbA1c | < 42 mmol/mol (6.0%) | Yes — diet, exercise, medication |
| Homocysteine | < 10 µmol/L | Yes — B6, B12, folate |
| Vitamin D | > 75 nmol/L | Yes — supplementation, sunlight |
| hs-CRP | < 1.0 mg/L | Yes — diet, exercise, sleep |
| TSH | 0.4 – 2.5 mIU/L | Yes — thyroid medication |
| Vitamin B12 | > 500 pg/mL | Yes — supplementation, diet |
8. What You Can Do Now to Protect Your Brain
You cannot get a dementia-specific blood test yet. But you can act on the modifiable risk factors that the research consistently links to cognitive decline. The Lancet Commission on Dementia estimates that up to 45% of dementia cases are attributable to modifiable risk factors.
EVIDENCE-BASED ACTIONS
- Test your blood. Check HbA1c, homocysteine, vitamin D, hs-CRP, thyroid and B12. These six markers cover the main modifiable metabolic risks to brain health.
- Optimise what's off. Low vitamin D? Supplement. Elevated homocysteine? B vitamins. High HbA1c? Dietary changes and exercise. These are not abstract recommendations — they are backed by intervention trials.
- Retest in 3–6 months. Verify the intervention worked. Blood markers shift measurably within weeks to months.
- Maintain cardiovascular health. What is good for the heart is good for the brain. Regular exercise, blood pressure control, healthy weight and not smoking are the strongest lifestyle protections against dementia.
- Watch the research. The NHS ADAPT trial results will start reporting from 2027. If p-tau217 proves clinically useful, it will likely be offered through NHS memory clinics before it reaches consumer testing.
CHECK YOUR BRAIN HEALTH MARKERS
All six biomarkers above are included in our panels
Our Essential and Performance panels include HbA1c, vitamin D, vitamin B12, hs-CRP, thyroid function and a full metabolic profile. Results in five days, reviewed by a GMC-registered doctor.
Frequently Asked Questions
Can you buy a dementia blood test in the UK?+
Not yet. p-tau217 blood tests are only available through NHS clinical trials. The ADAPT trial aims to bring them into routine NHS use by 2029. In the meantime, you can test blood markers linked to brain health — such as HbA1c, homocysteine, vitamin D and B12 — through private blood testing.
What is p-tau217?+
p-tau217 is a phosphorylated tau protein measured in blood. It reflects both amyloid plaque accumulation and tau tangle formation in the brain — the two hallmark pathologies of Alzheimer's disease. A 2026 Nature Medicine study showed it can predict symptom onset years to decades in advance.
Is the Galleri blood test for dementia?+
No. Galleri is a multi-cancer early detection test by GRAIL. It screens for signals from roughly 50 cancer types using cell-free DNA. It has nothing to do with dementia. The two are separate tests often confused in media coverage.
Which blood tests are good for brain health?+
Six standard blood biomarkers have strong evidence linking them to long-term brain health: HbA1c (blood sugar), homocysteine, vitamin D, hs-CRP (inflammation), thyroid function (TSH), and vitamin B12. All are modifiable — meaning if your levels are off, you can take action to reduce risk.
Can dementia be prevented?+
The Lancet Commission on Dementia estimates that up to 45% of dementia cases are attributable to modifiable risk factors. While there is no guaranteed prevention, managing blood sugar, inflammation, vitamin levels, thyroid function and cardiovascular health substantially reduces risk.
How much does a private blood test for brain health cost?+
Helvy's Essential panel starts at £149 and includes all six brain-health biomarkers discussed in this guide: HbA1c, vitamin D, vitamin B12, hs-CRP, thyroid function and a full metabolic profile. Results arrive in five days, reviewed by a GMC-registered doctor.