A blood test that predicts the risk of dying

As Canada's population ages, there is increasing demand on our health-care system. A simple blood test may help doctors predict who is at risk of imminent death, according to a study published Monday in the Canadian Medical Association Journal.

Dr. Stig Bojesen and colleagues from the University of Copenhagen studied 108,135 Danish people ages 20 to 100 years who were part of the Copenhagen General Population Study. During the study period, a total of 10,372 people died. The researchers combed through the health records of those who died in search of abnormal blood test results.

They found that the people who died during the study period had lower levels of a white blood cell called a lymphocyte. The researchers crunched the numbers. Compared with those with a normal lymphocyte count, those patients with a low lymphocyte count were 1.6 times more likely to die during the study period.

There are several possible ways in which a low lymphocyte count might be connected to an early demise. 

One clue is that the current study found that a low lymphocyte count was associated with an increased risk of death from cancer, cardiovascular disease, respiratory disease, infections and other causes. These are chronic diseases that are common in older patients.

Lymphocytes are part of the immune system and the immune system is necessary to help patients fight off chronic diseases. The researchers speculated that a weak immune system might be one of the reasons why diseases like cancer and respiratory disease are more common the older we get.

Another theory is that a low lymphocyte count might indicate that the patient is frail. We know from other research that frailty can lead to illness and death.

Other tests to predict risk of imminent death

The lymphocyte count is not the only blood test that can help predict the risk of dying.

A number of studies have looked at another simple blood test called C reactive protein or CRP. Elevated levels of CRP are associated with increased risk of imminent death. A recent study found that patients in Japan who come to the emergency department with a heart attack and who have a high CRP level are more likely to die during the ensuing hospital stay.

A 2019 study in the journal Nature Communications identified 14 new biomarkers that can be measured in the bloodstream that could predict the risk of dying within five or 10 years. The study found these tests would likely be more accurate than the conventional risk factors (for example, smoking and heart disease) that doctors use currently. 

The practical value of these kinds of tests to doctors in their work and to patients in their lives is still somewhat unclear.

The researchers say they hope the findings help doctors identify patients at risk of death within two years. Such patients might be followed more closely for signs of life-threatening illnesses and perhaps treated more aggressively. Patients could then be re-tested to see if the lymphocyte count, CRP and other blood tests returned to normal levels as the imminent risk of death is reduced.

Down the road, researchers say they would like to use those abnormal tests and biomarkers to design targeted treatments that might stave off death.
 
It's worth keeping in mind that studies like this one confirm what doctors already know. Studies show that doctors are good at identifying patients whose imminent death would not surprise them.

I think patients and their families might be very surprised that their doctors believe them at imminent risk of dying. I believe doctors need to share that information with patients and families to encourage them to live healthier or at very least prepare them for what lies ahead.