New Blood Test May Reveal Which Organs Are Ageing Faster

Your birthday records the number of years you have lived, but it cannot show whether your heart, brain or kidneys have coped with those years to the same extent.

This is because organs in one body may undergo biological ageing at different rates.

Organ ageing leaves distinct tissue signatures

A new study published in Nature Medicine indicates that ageing produces distinct changes in the microscopic structure of individual organs.

Researchers have used these signatures to create a method that could identify organs that appear older than expected from a single blood sample.

This is not currently a blood test that can be ordered through a hospital. It also cannot monitor an organ over years to measure its ageing rate directly. Rather, it estimates whether an organ seems biologically older or younger than would be expected for someone's chronological age.

A group led by André Rendeiro, with Ernesto Abila, Iva Buljan and Yimin Zheng as co-first authors, analysed 25,712 microscopic images of tissue from 983 deceased donors. The samples represented 40 tissue types from 29 organs.

Study authors André Rendeiro, Iva Buljan, Ernesto Abila and Yimin Zheng, from left to right. (Wolfgang Däuble/CeMM)

The team trained an artificial intelligence model using tissue samples from people of varying ages. As it learned, the system detected subtle age-related structural alterations, effectively building a “tissue clock” for each organ.

For instance, if the clock found that lung tissue from a 60-year-old resembled that of an older person, the lung was classed as older than expected.

On average, the models’ age predictions were around five years away from the donors’ real ages.

More intriguingly, the predictions seemed to capture something beyond a person’s date of birth.

Tissues judged to be older than expected were more likely to display structural changes and health conditions linked with ageing. These included tissue shrinkage, scar-like hardening, the disappearance of tiny blood vessels, fat build-up in skeletal muscle and nerve thinning.

Nor was there a single universal pattern of ageing across the body. Some individuals displayed advanced ageing in numerous organs, while others had one organ - such as the heart, lung or stomach - that looked substantially older than the rest of their body.

From tissue clocks to a blood-based organ-age test

Assessing an organ’s biological age directly generally involves an invasive procedure to obtain tissue.

To overcome that limitation, the researchers paired age estimates from tissue images with blood-sample gene-activity patterns from the same donors.

In straightforward terms, they sought shifts in gene activity in the blood that were associated with an organ looking older than expected.

“A blood sample does not directly image the organ; it estimates the organ's age gap through a learned correspondence,” André Rendeiro, a principal investigator at CeMM and the Ludwig Boltzmann Institute for Network Medicine at the University of Vienna, told ScienceAlert.

The researchers subsequently built a second model that used blood data alone to estimate the apparent ages of different organs. It performed best for whole-body ageing, the digestive system and the spleen.

To examine whether the estimates corresponded with actual disease, they applied the approach to blood data from healthy people and people with eight different medical conditions. In general, the models gave larger age gaps to the organs connected with each condition.

Among people who had had a stroke, the brain received the largest age gap from the model.

For people with Crohn’s disease, larger age gaps were assigned to the oesophagus, stomach, small intestine and colon.

Histological section of human cerebellum tissue used to investigate age-related shifts in tissue architecture. (Wolfgang Däuble/CeMM)

In the Alzheimer’s group, the brain was the sole organ with a significantly raised age gap.

These associations indicate that blood may contain hints about processes taking place deep within the body. Yet an organ appearing older does not establish that accelerated ageing caused a disease. Disease may have aged the organ, or the two processes may have arisen together.

Earlier blood-based approaches have estimated organ age by measuring proteins circulating in the blood.

One such study reported that an older-looking brain was linked to a greater risk of death.

However, current commercial biological-age tests may deliver very different results.

Limitations of the organ-ageing blood test

The new research also has significant limitations.

Most tissue samples were collected after death, and the team did not track the same individuals as they grew older. The blood-based approach was evaluated chiefly in people already diagnosed with a disease.

Whether the test could identify disease before symptoms appear is still unknown.

Prospective research, reliable performance in different populations and regulatory approval would all still be necessary. According to Rendeiro, clinical use is “realistically several years, possibly close to a decade,” away.

Related: Humans Age Faster at 2 Sharp Peaks, Research Shows

Abila, Iva Buljan, Yimin Zheng and Rendeiro disclosed competing financial interests through a patent related to the work.

For now, the findings indicate that representing biological age with a single number may overlook a key part of the picture.

Your heart, brain and kidneys inhabit the same body, but they may not experience time in the same way.

The study was published in Nature Medicine.

This article was fact-checked and edited by Fiona MacDonald. Although we take pride in our process, we are only human. If you notice an error, please let us know.