What does it mean to have high blood pressure? since blood pressure fluctuates all day, how is it correctly disgnosed?

PERSISTENTLY high.: You're right, blood pressure (BP) varies. But Hypertension is the condition characterized by PERSISTENTLY high BP. Screening is performed by recording BP> 140/90 mmHg after 5 min in a quiet dark room. (Pre-hypertension at 120/80). Normally, 5 min of rest will lower the BP to its lowest value. In hypertension, the BP is consistently elevated throughout the day. Ambulatory BP monitoring can confirm.