What is used to find someone's baseline blood pressure?

Establishing Baseline Blood Pressure

To find someone's baseline blood pressure, take multiple measurements on at least two separate occasions using proper technique, then average these readings—with out-of-office measurements (home or ambulatory monitoring) providing the most accurate baseline assessment. 1

Proper Measurement Technique

The accuracy of baseline BP determination depends critically on standardized measurement technique:

• Patient should be seated quietly for at least 5 minutes in a chair with back supported, feet flat on the floor, and legs uncrossed 1
• Arm must be supported at heart level with the cuff placed on bare skin 1
• Avoid caffeine, exercise, and smoking for at least 30 minutes before measurement 1
• Use an appropriately sized cuff with the bladder encircling at least 80% of the arm circumference 1

Office-Based Baseline Assessment

For establishing baseline BP in the office setting:

• Take at least two measurements, 1-2 minutes apart, and average them at each visit 1
• Measure BP in both arms at the first visit—if there is a >10 mmHg difference in systolic BP, use the arm with the higher reading for all subsequent measurements 1
• Obtain readings on at least two separate occasions before making diagnostic or treatment decisions 1
• The first reading should be discarded as it tends to be falsely elevated due to patient anxiety 2

A common pitfall is making decisions based on a single elevated reading—this leads to overdiagnosis and overtreatment of hypertension 1.

Out-of-Office Measurements: The Gold Standard for Baseline

Out-of-office BP measurements provide a more accurate baseline than office readings and should be used whenever possible:

Home Blood Pressure Monitoring (HBPM)

• Take two readings per session, 1-2 minutes apart 1, 3
• Measure twice daily (morning and evening) for at least 3 days, ideally 7 days 1, 3
• Average all readings to establish the baseline 1, 3
• An HBPM average of ≥135/85 mmHg corresponds to office BP of ≥140/90 mmHg 1

Ambulatory Blood Pressure Monitoring (ABPM)

• ABPM is considered the reference standard for establishing true baseline BP 4
• Measurements are taken every 15-30 minutes during the day and every 30-60 minutes at night over 24 hours 1
• A minimum of 70% usable readings (typically ≥27 measurements) is required for valid assessment 1
• The 24-hour average, daytime average, and nighttime average all contribute to baseline assessment 1
• ABPM predicts cardiovascular risk better than office BP 1

Why Multiple Measurements Matter

Blood pressure varies considerably throughout the day and between visits due to multiple factors including anxiety (white coat effect), activity level, and circadian rhythms 1, 5. A single measurement provides only a snapshot, not a true baseline.

• White coat hypertension (elevated office BP but normal out-of-office BP) occurs in approximately 10-15% of patients 1
• Masked hypertension (normal office BP but elevated out-of-office BP) also occurs and carries substantial cardiovascular risk 4
• Ambulatory BP monitoring identifies both conditions and provides the most accurate baseline 1

Equipment Requirements

• Use only validated BP devices—most devices on the market have not undergone proper validation testing 6
• Devices should be regularly calibrated and checked for accuracy (within 5 mmHg of mercury standard) 1
• Automated oscillometric devices reduce human error compared to auscultatory methods when used properly 4, 2

Special Populations

• In elderly patients, also measure BP in the standing position to assess for orthostatic hypotension (≥20/10 mmHg drop at 1 and/or 3 minutes after standing) 1
• In patients with atrial fibrillation, multiple auscultatory measurements are recommended as oscillometric devices may be inaccurate 1
• In children, BP should be measured in the right arm after 3-5 minutes of quiet rest, using age-appropriate cuff sizes 1