Telomere length test

Don't buy a consumer telomere test. Spend the money on established markers of inflammatory and metabolic health instead, such as high-sensitivity C-reactive protein (CRP), fasting insulin and a lipid panel. The one place a telomere test belongs is a specialist clinic, for people with lung scarring that runs in the family or unexplained bone-marrow failure.

What the test measures

Telomeres are stretches of repetitive DNA at the ends of each chromosome that shorten a little every time a cell divides; the biology is on Telomere attrition. There are two main ways to measure them:

• The PCR method. Almost all low-cost commercial kits use an assay based on the polymerase chain reaction (PCR), a DNA-amplification method. It reports only an average telomere signal relative to a reference gene, across millions of mixed cells. It is cheap and scalable, which is why almost all consumer kits use it.
• Flow-FISH (flow cytometry with fluorescence in situ hybridisation). A fluorescence technique that measures telomeres cell by cell in sorted white-cell types. It is the only telomere test validated for diagnosing genuine telomere diseases.^[1]

Why the cheap test can't track you

The PCR method is noisy. When ten laboratories measured the same blinded DNA samples, PCR results varied by about 20% from lab to lab, roughly twice as much as older gel-based methods, and the absolute numbers could not be compared directly between labs. Most labs still ranked the samples in a similar order, and once results were converted to a common scale PCR was no less accurate than the older methods.^[2] That makes it usable for comparing groups in research, not for reading one person's result. Even within one lab, repeat runs of the same sample varied by about 16% on average.^[3]

For a healthy adult the consequences add up. There is no agreed reference range, the year-to-year change in one person is swamped by assay noise, and "watching your telomeres improve" on a supplement is measuring mostly random variation.

The PCR method also misses cases where it matters most. In a small study of people being tested for a suspected telomere disease, it correctly flagged only 40% of those whose telomeres were below the tenth percentile, against 80% for flow-FISH. Both methods caught every case of extremely short telomeres, so the PCR method's misses fall in the short-but-not-extreme zone, where a borderline result is hardest to interpret.^[4]

Even a good measurement predicts poorly

The problem is not only the assay. Measured carefully in research cohorts, blood telomere length is a weak predictor. Tracked against later deaths in three US cohorts, DNA-methylation "clocks" did better than telomere length, and telomere length did not even point the same way in every cohort.^[5] In a Scottish cohort of older adults followed for 16 years, every aging marker tested was linked to risk of death except telomere length.^[6]

Longer is not simply better either: people who inherit longer telomeres get fewer of some degenerative diseases but more cancers and some other conditions, such as high blood pressure, so a "good" number has no clear meaning.^[7]

Who promotes it

Some of the most prominent scientific advocacy for telomere testing comes from researchers with a direct commercial stake in it. María Blasco, among the field's leading telomere biologists, co-founded Life Length, a company that sells telomere-length measurement. The interest is disclosed in the declarations of the 2023 hallmarks paper she co-authored, alongside a review of hers arguing for telomeres as a clinical target.^[8] That doesn't make the science wrong, but it is a reason to discount marketing that frames a noisy number as an actionable readout of your aging.

When testing does make sense

Testing matters for people who may have an inherited telomere biology disorder: those with lung scarring (pulmonary fibrosis) that runs in the family, or with unexplained bone-marrow failure. Here the clinical-grade flow-FISH test, alongside specialist genetic testing, earns its place.

What to do

1. Skip consumer telomere tests, including ones bundled with supplements that claim to lengthen telomeres.
2. Measure what you can act on instead: high-sensitivity CRP, fasting insulin and a lipid panel.
3. If lung fibrosis runs in your family, or you have unexplained bone-marrow failure, ask a specialist about genetic testing and flow-FISH.

Further reading

• Martin-Ruiz CM, et al. Reproducibility of telomere length assessment: an international collaborative study. Int J Epidemiol 2015.^[9]
• Gutierrez-Rodrigues F, et al. Direct comparison of flow-FISH and qPCR as diagnostic tests for telomere length measurement in humans. PLoS One 2014.^[10]
• Franke M, et al. Diagnosis and management of adult telomere biology disorders. Haematologica 2026.^[11]
• Beydoun MA, et al. Telomere Length, Epigenetic Age Acceleration, and Mortality Risk in US Adult Populations: An Additive Bayesian Network Analysis. Aging Cell 2025.^[12]
• Pyrgioti M, et al. Multimodal Ageing Biomarkers and Plasma Proteomic Signatures Associated With All-Cause Mortality. Aging Cell 2026.^[13]
• Bär C, Blasco MA. Telomeres and telomerase as therapeutic targets to prevent and treat age-related diseases. F1000Res 2016 — note the disclosed commercial interest in telomere measurement.^[14]