Taking a person's blood pressure during the daytime and at night could detect potentially fatal complications, a study suggests.
It means BP should be monitored for a full 24-hour period to give the best indication of any complications, the research in The Lancet added.
Scientists at the University of Leuven in Belgium studied more than 7,400 people across six countries. The subjects had an average age of 56.8 years, and were followed up for around 10 years.
They found daytime blood pressure adjusted for night-time blood pressure can predict fatal and serious cardiovascular events.
But antihypertensive drugs might hide the correlation in some patients, they added.
They also found that patients with systolic night-to-day ratio values of one or more were older, at higher risk of death, and died at an older age than those whose night-to-day ratio was normal - between 0.8 and 0.9.
The authors conclude: "Our findings have implications for clinical practice and research.
"The night-time blood pressure predicted mortality and nonfatal outcomes, irrespective of treatment status.
"The daytime blood pressure independently predicted the composite of all fatal and nonfatal cardiovascular events, especially in untreated participants.
"Our findings therefore support recording the ambulatory blood pressure during the whole day."