Biological age Preprint

A “biological age” from routine hospital blood tests was linked to how patients fared after heart surgery

In about 4,000 heart and chest surgery patients at one New York hospital, those whose ordinary lab results made them look biologically older were more likely to die or have complications after the operation. But the score added little to the risk scores surgeons already use. It is an observational, not yet peer-reviewed preprint.

Two patients of the same age can come out of the same operation very differently. A team at Columbia University Irving Medical Center in New York asked whether a biological age score, calculated from blood tests that hospitals already run every day, could tell such patients apart. In heart and chest surgery patients it did, to a point: a higher score was linked to more deaths and complications. The study is observational, comes from a single hospital and is a preprint, not yet peer-reviewed.

Biological age scores of this kind turn a set of ordinary lab values (kidney and liver tests, blood sugar, blood cell counts) into an "age" at which that pattern of results is typical. People who come out older than their calendar age tend, in research studies, to get sick and die sooner. But those formulas were built in research volunteers; nobody knew whether the messy lab results of real hospital patients would give meaningful numbers.

What they did

  • Building the score. Using NHANES III, a large US health survey from 1988–1994 with about 22 years of follow-up, and the method behind the well-known PhenoAge score, a statistical model picked 18 common lab tests (for example albumin, creatinine, glucose and white blood cell count) that together best predicted death. It was checked in a later round of the survey.
  • The patients. Records of 4,313 adults who had cardiothoracic surgery (operations on the heart and other organs in the chest) between 2020 and 2024 were linked to the hospital's surgery registry, where complications are recorded and checked by hand.
  • Before surgery: 3,343 patients had lab results from the six months before their operation. The team asked whether their biological age predicted death within 30 days and complications such as stroke, kidney failure, sepsis (a dangerous body-wide reaction to infection) and needing a breathing machine for a long time.
  • After surgery: 3,991 patients had lab results in the first 48 hours in intensive care. Here the questions were how long they stayed in intensive care and whether they died before leaving hospital.

All analyses took calendar age and sex into account.

What they found

  • The score worked on hospital data. Biological age tracked calendar age closely (a correlation of 0.82). On average patients came out 3.3 years younger than their calendar age, perhaps because people age more slowly today than in the 1990s survey, or because lab methods changed.
  • Biologically older before surgery, worse outcomes. For each step up in biological age (one standard unit), the risk of dying within 30 days was about 1.6 times higher. Sixty-one patients died in that time. Complications were also more common, with risks 1.12 to 1.54 times higher per step, and the pattern was similar in men and women.
  • Little gain over existing tools. About two thirds of patients also had a risk score from the Society of Thoracic Surgeons, a detailed, hand-collected calculation that surgeons already use. The biological age was only partly related to it, but adding it improved predictions only for sepsis.
  • After surgery, the trend mattered. In intensive care, biological age first dipped and then crept back, driven by values like blood sugar and bilirubin that shift with the stress of surgery. Patients who were biologically older in those 48 hours stayed longer in intensive care and were more likely to die in hospital, and so were those whose score rose faster. Knowing only age and sex sorted patients who would die in hospital from those who survived only modestly (an accuracy measure of 0.66, where 0.5 is a coin toss and 1 is perfect); adding the biological age measurements raised it to 0.85.

What to keep in mind

  • One hospital, one kind of surgery. The authors say the results need to be repeated in other health systems and other groups of patients before anyone can say they apply more widely.
  • Not everyone had the tests. Only patients with enough recent lab results could be scored, and they may differ from the rest.
  • A limited lab menu. Some tests that help in research versions of the score were rarely available in the records, so the team calls its results "a conservative estimate".
  • Prediction, not proof of cause. This is an observational study: a high score was linked to worse outcomes, nothing more, and a sick patient's lab values partly reflect the illness itself. The high accuracy after surgery was measured in the same patients the models were fitted on, not in a separate group.
  • The existing score already does the job. Where it was available, biological age added almost nothing; its advantage is that it can be computed automatically for everyone.
  • Interests. Some of the researchers are inventors of other aging measures that are licensed to a company for commercial use.

Why it matters

Yesterday we wrote about a similar study in cancer surgery patients, which found that a PhenoAge score there may mostly reflect the cancer. This study is a more hopeful but still cautious counterpart: a biological age computed silently from records a hospital already has gave sensible numbers and was linked to how patients recovered. It does not beat the risk scores that surgeons use today, and nobody should read their own lab results this way. What it shows is that aging research measures can be calculated inside real hospital systems, which is the first step toward testing whether they help doctors at all.

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