A simple blood test could predict if a person is likely to die - even if they are not ill.

Researchers said they were astonished to discover the "death test", which predicts the chance of a healthy person dying from a medical condition within five years.

They found that the levels of four "biomarkers" in the body, indicated a general level of "frailty". People whose biomarkers were out of kilter were five times more likely to die within five years of the blood test.

"What is especially interesting is that these biomarkers reflect the risk for dying from very different types of diseases such as heart disease or cancer. They seem to be signs of a general frailty in the body," said Dr Johannes Kettunen of the Institute for Molecular Medicine in Finland.

"In the future these measures can be used to identify people who appear healthy but in fact have serious underlying illnesses and guide them to proper treatment."

A biomarker is a molecule found in blood, body fluids, or tissues that signals an abnormal process, condition, or disease. For example, cholesterol levels are measured to assess the risk of heart disease.

Blood samples from over 17,000 generally healthy people were screened for 100 biomarkers, and those people monitored over five years.

In that time, 684 died from illnesses including cancer and cardiovascular disease. They all had similar levels of four biomarkers: albumin; alpha-1-acid glycoprotein; citrate, and a similar size of very-low-density lipoprotein particles.

One in five with the highest biomarker scores died within the first year of the study.

Professor Markus Perola said: "It was astonishing that these biomarkers appeared to actually predict mortality independent of disease. These were all apparently healthy people but to our surprise it appears these biomarkers show an undetected frailty which people did not know they had." The study was published in PLOS Medicine.

Daily Telegraph, London