High blood pressure is a symptom and is not always caused by disease. It may be measured as higher than normal in incidental states or factors, such as after exercise, taking certain medications, emotional effects, etc. After removing these factors that cause elevated blood pressure, the blood pressure can be reduced to normal values.
In contrast, the diagnosis of hypertensive disorders requires the measurement of blood pressure on several occasions and on different days.
A systolic blood pressure of ≥140mmHg and/or a diastolic blood pressure of ≥90mmHg measured three times on different days is diagnostic of hypertension.
Hypertension is also diagnosed if the patient has a previous history of hypertension and is taking blood pressure lowering medication, although the blood pressure is normal.