The most validated blood-based biological age algorithm is PhenoAge, built at Yale in 2018 and tested against 23 years of mortality data. It uses nine ordinary blood markers, not an exotic panel. Every one of them sits in a standard comprehensive blood test. This page explains what those nine are, how blood-based ageing compares to epigenetic clocks, and the 2024 finding that complicates the clock story considerably.
Morgan Levine and colleagues at Yale used NHANES III data covering 9,926 adults with more than 23 years of mortality follow-up. They identified nine clinical blood markers which, combined with chronological age, predict 10-year survival with roughly 90% accuracy. PhenoAge was subsequently paired with DNA methylation data to produce DNAm PhenoAge, but the underlying phenotypic model runs on blood chemistry alone.
What is striking about the list is how unexotic it is. There is no proprietary marker and nothing that requires a specialist assay. These are components of a full blood count, a liver panel, a kidney panel and an inflammation marker.
Liver synthetic function and nutritional status. Declining albumin is associated with frailty and mortality risk independent of other markers.
Kidney filtration. Rises as renal function declines, though it is confounded by muscle mass and creatine supplementation.
Metabolic regulation. Fasting glucose captures the current state of glycaemic control.
Systemic inflammation. The single marker in the set most responsive to lifestyle intervention.
Immune composition. Declining lymphocyte proportion is a recognised feature of immune ageing.
Average red blood cell size. Shifts with B12 and folate status and with chronic disease.
Variation in red cell size. One of the more surprising mortality predictors in the literature, and rarely discussed outside it.
Liver and bone turnover. Elevated ALP is associated with a range of age-related pathology.
Overall immune activity. Both elevation and suppression carry risk signal at the extremes.
PhenoAge compares your phenotypic profile against your actual age. The output is the gap between them, not an absolute number in isolation.
Worth knowing before you buy anything: all nine of these markers appear in the TrueVitals Ultimate panel, and in most genuinely comprehensive blood panels. If you already have recent comprehensive bloods, you likely already hold the inputs. You do not need a specialist biological age product to obtain the underlying data.
Epigenetic clocks are usually presented as the gold standard for biological age, and first-generation clocks like Horvath's are the ones most often cited. A 2024 analysis is worth knowing about before you spend several hundred pounds on one.
Researchers built simulation models of DNA methylation change and tested them against 22,770 sorted and whole-blood samples across 25 independent cohorts. They found that approximately 66 to 75% of the accuracy underpinning Horvath's clock could be driven by a stochastic process — that is, by essentially random methylation drift rather than by biological ageing. For Zhang's clock, which is more accurate at predicting chronological age, the figure rose to 90%.
For PhenoAge the figure was lower, at 63%. The authors concluded this suggests biological ageing is reflected by non-stochastic processes, and that clocks trained on health outcomes rather than on chronological age capture more genuine signal.
This does not make epigenetic testing worthless. Second and third-generation clocks such as GrimAge and DunedinPACE were trained on mortality and pace-of-decline rather than on age, and they predict outcomes independently of traditional risk factors. But it does mean the intuitive assumption that a bigger number of methylation sites equals a better answer is not well founded. A test analysing 900,000 sites is not automatically more informative than one built on nine well-chosen blood markers.
Four ways to estimate biological age, compared on what they measure, how fast they respond to change, and what they cost in the UK.
| Method | What it measures | Validation | Responds to change | Actionable | Typical UK cost |
|---|---|---|---|---|---|
| Blood biomarkers (PhenoAge) | Organ function, inflammation, metabolic and immune status | NHANES III, 9,926 adults, 23yr follow-up | Weeks to months | High | Included in a comprehensive panel |
| Second/third-gen epigenetic (GrimAge, DunedinPACE) | Methylation signatures trained on mortality and pace of decline | Strong, predicts outcomes independently | Months to years | Moderate | £300-600 |
| First-gen epigenetic (Horvath, Hannum) | Methylation trained on chronological age | Predicts age well, health outcomes less so | Slow | Low | £200-400 |
| Telomere length | Chromosome cap length | Weak individual predictive value | Slow, high measurement variability | Low | £100-250 |
Saliva-based epigenetic testing is materially less reliable than blood-based, because saliva contains a mix of epithelial cells, white blood cells and bacteria which introduces noise into methylation measurement. Published comparisons indicate saliva results can vary by up to 25 years against blood.
TrueVitals tests blood biomarkers. We do not offer DNA methylation testing, and this page is not an argument that epigenetic clocks are worthless. They measure something real that blood chemistry does not capture directly.
If you specifically want an epigenetic clock reading — a DunedinPACE pace-of-ageing score, organ-specific ages, or GrimAge — you need a dedicated methylation test and we are not the provider. Choose a blood-based one rather than saliva, and prefer a second or third-generation clock over Horvath or Hannum.
If your goal is to change something, blood markers are the better tool and it is not close. They respond within weeks. You can measure hs-CRP, alter training, sleep and diet, and see a real difference at your next draw eight to twelve weeks later. Methylation patterns move over months to years, which makes them a poor feedback loop even where the underlying science is sound.
The most defensible position, if you want one, is that blood biomarkers tell you what is happening in your body now and whether your interventions are working, while epigenetic clocks offer a slower-moving estimate of accumulated biological change. They answer different questions. Most people asking about biological age want the first one.
PhenoAge is a mortality-prediction model, not a complete health picture. It was built to answer a narrow question well. Several markers with strong evidence behind them sit outside it, and a comprehensive panel gives you both.
Atherogenic particle count and inherited cardiovascular risk. The 2026 AHA/ACC guidelines now recommend ApoB measurement. Neither is in the PhenoAge nine, and neither is tested by the NHS.
PhenoAge uses fasting glucose, which moves late. Fasting insulin catches insulin resistance years earlier, while it is still reversible.
PhenoAge uses CRP. High-sensitivity CRP resolves the low-grade chronic inflammation range that standard CRP cannot, which is the range that matters for ageing.
Thyroid function shapes metabolic rate, energy and body composition. Not in PhenoAge, and frequently not run by NHS labs beyond TSH.
Testosterone, oestradiol and DHEA-S decline with age and affect muscle mass, bone density, cognition and mood. Absent from PhenoAge entirely.
Associated with endothelial damage and cognitive decline, and correctable with B vitamins. One of the more actionable markers in ageing, and not in the nine.
This is the argument for a comprehensive panel over a biological age product. A single composite score compresses a great deal into one number. The underlying markers, read together, tell you which system is actually drifting and what to do about it. The full longevity marker set.
All nine PhenoAge markers are in the Ultimate panel at £349, alongside ApoB, Lp(a), fasting insulin, HOMA-IR, hs-CRP, homocysteine, full thyroid with antibodies, complete hormones with SHBG, full iron studies and cystatin C. 114 biomarkers in total, with AI cross-system analysis and medical professional review, delivered in 4 working days.
The Signature panel at £799 tests 230 markers through Randox Health laboratories and adds neurological markers, digestive and gastric health, extended autoimmune and tumour screening, Epstein-Barr antibodies, and physical measurements taken at your appointment: blood pressure, weight, waist and hip circumference and resting pulse. Those physical measurements matter here, because several of the strongest ageing predictors identified by the 2025 international Delphi panel are physical rather than biochemical.
Neither includes a DNA methylation reading, and neither presents a single biological age number. What you get is the underlying data, read as a system, with the trends visible once you have tested more than once.
Yes. PhenoAge uses nine standard blood markers plus chronological age: albumin, creatinine, glucose, CRP, lymphocyte percentage, mean cell volume, red cell distribution width, alkaline phosphatase and white blood cell count. Validated on NHANES III data from 9,926 adults with 23 years of follow-up, predicting 10-year survival with roughly 90% accuracy. All nine appear in a comprehensive blood panel.
They measure something different rather than something strictly better. A 2024 study across 22,770 samples found 66 to 75% of Horvath clock accuracy could be explained by a stochastic process, rising to 90% for Zhang's clock but falling to 63% for PhenoAge. Second and third-generation clocks like GrimAge and DunedinPACE are stronger, but cost more and move slowly.
Considerably less accurate than blood. Saliva contains a mix of epithelial cells, white blood cells and bacteria, which introduces noise into methylation measurement. Published comparisons indicate saliva results can vary by up to 25 years against blood-based testing. If you buy an epigenetic test, buy a blood-based one.
No. We test blood biomarkers, not methylation. The Ultimate panel at 114 markers and Signature at 230 include all nine PhenoAge markers alongside the wider set covering organ function, metabolic health, inflammation and hormones. For an epigenetic clock reading specifically, you need a dedicated methylation provider.
Blood biomarkers, clearly. They respond within weeks to months, so you can measure, intervene, and remeasure eight to twelve weeks later to see whether it worked. Methylation and telomere length shift far more slowly, making them poor feedback tools. Why trends beat single readings.
The unglamorous answers. Cardiorespiratory fitness and strength training have the strongest evidence of anything measurable. Beyond that: managing ApoB, keeping fasting insulin low, reducing chronic inflammation, sleeping properly, and not smoking. Supplements move markers at the margins. Nothing in the evidence base outperforms fitness. Training and blood markers.
Every PhenoAge input plus ApoB, Lp(a), fasting insulin, HOMA-IR, hs-CRP and homocysteine. 114 biomarkers, AI cross-system analysis, medical review, 4 working days.
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