A new blood test can measure the activity levels of certain genes to give researchers an indication of how fast someone is ageing, giving them an accurate measure of their 'biological age', which can often be at odds with their 'chronological age'. 

The team behind the test say the results could help doctors to more accurately predict and diagnose Alzheimer's disease, or even figure out how healthy donated organs are. "We use birth year, or chronological age, to judge everything from insurance premiums to whether you get a medical procedure or not," one of the researchers, James Timmons from King's College London, told Steve Connor at The Independent. "Most people accept that all 60-year-olds are not the same, but there has been no reliable test for underlying biological age."

Research has shown that how long we've been on the planet isn't actually the best measure for how we are ageing in a biological sense. Back in July, a study investigated this by using specific markers to come up with a person's biological age, including blood pressure, organ function, metabolism, cholesterol levels, and cardiovascular fitness. By looking at these measurements over time, the researchers came up with a 'rate of ageing' for each participant.

As David Nield reported for us at the time, "The biological ages across the group of 38-year-olds varied from a youthful 28 to a creaky 61," with individuals who happened to age quickly being less physically able, showing cognitive decline and brain ageing, self-reporting worse health, and looking older, even before middle age. 

Timmons and his team used a different approach to come up with what they call "the first robust molecular 'signature' of biological age in humans". Basing the test on the stark differences they could see in people with mild cognitive impairment and healthy people, they took samples from 65-year-old volunteers and measured the levels of RNA in 150 key genes. 

According to BBC news, these 150 genes were whittled down by first comparing 54,000 markers of gene activity in healthy, but not super-active, 25- and 65-year-olds. 

"There's a healthy ageing signature that's common to all our tissues, and it appears to be prognostic for a number of things including longevity and cognitive decline," Timmons told the BBC. "It looks like from the age of 40 onwards you can use this to give guidance on how well an individual is ageing."

They repeated the process working with 70-year-old volunteers and correlated what they found to over two decades of their volunteers' health records. Publishing the results in Genome Biology, they report that a higher level of gene activity, measured through RNA, was linked to better kidney and cognitive function over a 12-year period. 

Practical applications for this test lie in how measurements of gene activity were the same in both the brain and blood of people with Alzheimer's disease, which means a simple blood test rather than a test that probes brain activity could give doctors an accurate picture of what's going on.

"This is the first blood test of its kind and has shown that the same set of molecules are regulated in both the blood and the brain regions associated with dementia, and it can help contribute to a dementia diagnosis," Timmons told The Independent. 

The researchers also plan to use the test on organ transplants in the UK to see if it can identify biologically 'young' and healthy organs from people who are chronologically old.

Of course, the obvious ethical problem with having another marker for a person's age is what insurance companies will end up doing with that information if they ever get a hold of it, but at this stage, it seems that knowing that much about ourselves only helps us to better understand what health risks we could be facing as we hit middle age and beyond.