What is the method to calculate average blood pressure from 7-day readings?

Calculating Average Blood Pressure from 7-Day Readings

To calculate the average blood pressure from 7-day readings, take all systolic and diastolic measurements separately, add them together, and divide by the total number of readings.

Proper Home Blood Pressure Monitoring Protocol

Preparation

• Use a validated upper-arm oscillometric device 1
• Rest quietly for 5 minutes before taking readings 2
• Avoid caffeine, exercise, and smoking for at least 30 minutes before measurement 2
• Empty your bladder before measuring 2
• Sit with back supported, both feet flat on floor 2
• Position arm at heart level with support (e.g., resting on desk) 2
• Remove clothing from arm where cuff will be placed 2

Measurement Technique

• Use correct cuff size (bladder should encircle 80% of arm) 2
• Position middle of cuff on upper arm at heart level 2
• Take measurements twice daily - morning and evening 2
• Take 2-3 readings at each session, 1-2 minutes apart 2
• Remain quiet during measurements (no talking) 2

Recording and Calculating

1. Record all readings without selection bias 2
2. For a 7-day monitoring period:
   • Discard the first day's readings (to account for adjustment period) 2
   • Use readings from days 2-7 for calculation 2
   • Calculate separate averages for systolic and diastolic readings 2
   • Formula: Sum of all readings ÷ Number of readings = Average BP

Example Calculation

If you have 2 readings in the morning and 2 in the evening for 7 days:

• Total readings: 28 (4 readings × 7 days)
• Usable readings: 24 (4 readings × 6 days, excluding first day)
• Average systolic = Sum of all systolic readings ÷ 24
• Average diastolic = Sum of all diastolic readings ÷ 24

Interpretation of Home BP Averages

• Hypertension threshold: Average home BP ≥135/85 mmHg 2
• Elevated BP threshold: Average home BP 120-134/70-84 mmHg 2
• Normal BP: Average home BP <120/70 mmHg 2

Important Considerations

• The average of multiple readings is more clinically significant than individual high or low readings 1
• Ensure device accuracy by comparing with clinical readings annually 1
• Bring your home BP monitor to office visits to verify accuracy 1
• Avoid taking additional readings when feeling stressed as this can bias your average 1
• Oscillometric devices may not work well in patients with atrial fibrillation 1

Following this standardized protocol ensures accurate home blood pressure monitoring and provides reliable data for clinical decision-making regarding hypertension management.