4. To rule out white-coat effect：It has been reported that 20%-30% of patients with apparent resistant hypertension referred for ambulatory BP monitoring in fact have normal BP readings[5].When patients have higher BP levels than 140 over 90 mmHg when measured by the physician than when assessed at home or with AMBP( ambulatory monitoring blood pressure) which is called white-coat hypertension. The patients with white-coat hypertension have less severe target organ damage and cardiovascular risk than those with persistent elevated blood pressure in ambulatory monitoring.