Can a blood test reveal how old your organs are?

Blood tests that say something about how your body is ageing already exist, but they do not measure 'organ age' the way a number appears on a scale. They look at proteins in your blood that are released when cells age and in doing so secrete a cocktail of substances. A study involving more than a thousand participants showed that such proteins, measured in blood plasma, are associated with typical ageing characteristics: how much body fat you carry, what your blood lipids look like, and how well you can walk. These are broad signals of biological ageing, not a picture of one specific organ.

The associations are correlational: people with more of these ageing proteins in their blood show, on average, more ageing-related characteristics, but the tests do not tell you whether it is your heart, liver or kidneys that 'feel' old. The researchers themselves call them 'potential biomarkers' and explicitly state that further clinical studies are needed before this can be put to practical use.

A second study took a different approach: it looked for blood markers that can detect osteoarthritis (joint wear) and can even distinguish between younger and older patients with osteoarthritis. Five proteins together scored very highly in recognising osteoarthritis versus no osteoarthritis. But this too is a diagnostic model for a specific condition, not a general ruler for organ age. Moreover, it has not yet been tested on an independent group of patients, which is a serious limitation.

In summary: blood testing can map biological ageing processes, but the translation to 'your liver is 58 years old' has not yet been made. That level of precision does not yet exist. If you want to assess your biological condition, clinically validated measures such as blood pressure, blood glucose and bone density are currently more reliable than commercial 'organ age tests'.