A study by the US National Heart, Lung, and Blood Institute (NHLBI) found that systolic blood pressure, far more than diastolic blood pressure, identifies patients with hypertension, determines their blood pressure stage, and indicates the need for treatment.

The research, published in the journal Hypertension, concludes that it is important to take note of both systolic and diastolic blood pressure readings.

Systolic pressure measures the force blood exerts on the artery walls when the heart beats, and diastolic pressure measures the force on the arteries between heartbeats.

Dr Claude Lenfant, NHLBI director, said: "The message from this study is that you cannot ignore systolic pressure.

"For years, treatment strategies have focused on lowering a patient's diastolic pressure, because diastolic pressure accurately predicted heart disease and stroke risk in younger patients.

"But this practice excludes the elderly, who tend to have higher systolic pressures and lower diastolic pressures - and who have the least-controlled blood pressure of all patients."

Definition of hypertension

Hypertension is diagnosed when the systolic blood pressure is 140 mm Hg or higher or the diastolic blood pressure is 90 mm Hg or higher.

Patients are classified into stages of hypertension depending on how high or low their blood pressure is.

The researchers examined nearly 5,000 untreated men and women, average age 58, and determined each person's blood pressure stage using both systolic and diastolic pressure together.

They then compared these blood pressure stage classifications with those obtained from using only the systolic pressure or only the diastolic pressure.

They found that systolic blood pressure alone correctly classified the blood pressure stage in about 96% of patients, while diastolic pressure alone classified only 68% of patients correctly.

Among patients over age 60, researchers found that systolic pressure alone correctly classified 99% of patients, whereas diastolic alone correctly classified only 47 percent.