Home blood pressure measurement has been recommended to use in the diagnosis of hypertension. The investigators have developed diagnostic algorithm of hypertension by using 24-hour and home blood pressure measurement. However, the diagnostic agreement between home blood pressure measurement and 24-hour ambulatory blood pressure measurement is about 70 - 85%. The discrepancy of diagnosis between home blood pressure measurement and 24-hour ambulatory blood pressure is one of the barriers to introduce home blood pressure measurement in the diagnosis of hypertension.

To solve the discrepancy, identifying the characteristic patients showing discrepancy of hypertension diagnosis between home blood pressure measurement and 24-hour ambulatory blood pressure measurement is needed.

The purpose of the present study are (1) to validate the diagnostic algorithm of hypertension by using 24-hour ambulatory blood pressure and home blood pressure measurement the investigators have developed, and (2) to identifying the characteristics of patients showing discrepancy of diagnosis between 24-hour ambulatory blood pressure and home blood pressure measurement, and (3) lastly to improve the diagnostic algorithm of hypertension by using home blood pressure measurement.

Inclusion Criteria:

• Men and women
• Patients with high blood pressure measured by doctors at the outpatient office

Exclusion Criteria:

• Patients taking antihypertensive drugs or blood pressure affecting drugs within 1 month
• Secondary hypertension
• Hypertensive emergency and urgency
• Severe heart failure (NYHA III and IV)
• Angina with 6 months
• Myocardial infarction within 6 months
• Peripheral artery disease within 6 months
• Significant arrhythmia (i.e. ventricular tachycardia and fibrillation, atrial fibrillation, atrial flutter)
• Pregnancy
• Night labor, shift worker
• Those who are currently participating in other clinical studies
• Those who have taken other clinical trial drugs within the past month
• According to the opinion of the researcher, those who have or may have a disease that may interfere with the completion of the study
• History of drug or alcohol dependence within 6 months

At the out-patient clinics, study investigators recruit study participants who have high blood pressure measured by them at the out-patient clinics and adequate for eligibility.

In order to share the individual participant data, the informed consent from the research participants is required un the Korean law, and we did not get the consent to share at the beginning of this study.