Imagine taking two biological-age tests and receiving two different results.
One says your biological age is 48. Another says it is 53.
How can both tests be measuring biological age and give different answers?
The reason starts with how biological age is estimated.
There is currently no single test that directly measures biological age. Instead, different methods use selected biomarkers of aging and combine them using statistical or computational models.
The biomarkers used can differ considerably.
One method may use clinical measurements such as blood pressure, glucose, cholesterol, kidney function or other routine blood markers. Another may analyze DNA methylation, while other approaches can use different molecular data or even medical imaging.
Other approaches can analyze larger and more complex biological datasets.
The calculation method can differ too.
Even when researchers use similar biological measurements, different mathematical models may combine and interpret that information differently. Studies comparing biological-age methods have found that their performance varies between populations and between the health outcomes being studied.
This means that a difference between two biological-age results does not necessarily tell us that one test is correct and the other is wrong. The tests may be based on different biological information or different methods of calculating the result.
For this reason, a biological-age number is easier to interpret when we know what was measured, how the result was calculated and what the method has been shown to predict.
At present, biological-age tests should not be assumed to be interchangeable.
