Lower levels of lymphocyte blood cells could be an early warning for future illness, according to a Danish study which found that low counts were associated with a 60 per cent increase in death from any cause.
Lymphopenia -- a condition where levels of lymphocyte blood cells are low -- is often detected during routine blood tests, the researchers said.
Patients are not usually referred for further investigation because the value of the condition as a predictor of future health was not known, they said.
"Our study showed that participants with lymphopenia were at high risk of dying from any cause, regardless of any other risk factor for all-cause mortality including age," said Stig Bojesen, from Copenhagen University Hospital in Denmark.
The study, published in the Canadian Medical Association Journal, included 108,135 people of Danish descent aged 20-100 years.
They were enrolled in the Copenhagen General Population Study between 2003 and 2015.
Low lymphocyte count was associated with a 1.6-fold increase in the risk of death from any cause and a 1.5- to 2.8-fold increased risk of death from cancer, cardiovascular disease, respiratory disease, infections and other causes, the researchers said.
During the study period, a total of 10,372 people died, they said.
According to the researchers, older age was associated with decreasing lymphocyte counts.
The link between lymphopenia and death may be because of reduced immune capacity to survive potentially lethal diseases, they said.
Lymphopenia could also indicate frailty which could lead to illness and death, the researchers said.
They hope their findings may help doctors identify at-risk people.
"Using the absolute 2-year risks of all-cause mortality, physicians can identify high-risk individuals with lymphopenia (e.g., smokers older than 80 years) who might benefit from additional surveillance," the researchers noted.