When self‑monitoring blood pressure at home, should the patient record the highest, lowest, or average reading?

Home Blood Pressure Recording Protocol

Patients should record ALL readings from days 2-7 and calculate the average of these values—never select only the highest or lowest readings. 1, 2

Core Recording Principle

The fundamental rule is to record every single measurement without selection or omission. 2 Studies demonstrate that more than half of patients who self-monitor will fabricate or omit readings when given devices without memory storage, which completely invalidates the data. 1 This is why current guidelines mandate using validated devices with automatic memory storage to prevent selective reporting. 1, 2

Standard Measurement Protocol

Equipment and Timing

• Use a validated automated oscillometric upper-arm device with memory storage 1, 2
• Measure twice daily (morning and evening) for 7 consecutive days 1, 2
• Take 2 readings per session, spaced 1-2 minutes apart 1, 2
• Morning: immediately after waking, after urination, before breakfast and before taking antihypertensive medication 1, 2
• Evening: before dinner or at a consistent pre-specified time 2

Data Handling

• Discard all readings from day 1 (they show greater variability) 2, 3
• Record all remaining readings from days 2-7 (minimum 12 morning + 12 evening = 24 total readings) 1, 2
• Calculate the average of ALL these readings—this average is your reference value for clinical decisions 1, 2

Why Averaging Matters

Home blood pressure is inherently variable due to neural, mechanical, and humoral factors. 1 A single reading—whether high or low—has minimal clinical significance. 1 The strength of home monitoring lies in obtaining large numbers of readings that eliminate the white-coat effect and provide superior reproducibility compared to office measurements. 1, 4

Research shows that averaging at least 12-30 readings provides the most reliable estimate of true blood pressure, with maximal reduction in measurement error. 1, 3 The correlation with 24-hour ambulatory monitoring improves significantly when using this averaging approach, particularly when the first day is excluded. 3

Diagnostic Thresholds

• Hypertension: average home BP ≥135/85 mmHg (equivalent to office BP ≥140/90 mmHg) 1, 2
• Elevated BP: average 120-134/70-84 mmHg 1

These thresholds are based on the average of multiple readings, not individual high or low values. 1

Critical Pitfalls to Avoid

• Never cherry-pick readings based on how you feel or which values seem "better"—this invalidates the entire dataset 2
• Do not take extra measurements when feeling stressed or symptomatic, as this introduces selection bias 2
• Do not base clinical decisions on a single day of measurements—they lack reliability 2
• Avoid devices without memory storage, which enable selective reporting and misrepresentation of true BP patterns 1, 2

Clinical Application

Bring the device with stored readings to every clinic appointment so your healthcare provider can download and review the complete dataset. 2 The averaged home BP predicts cardiovascular events and mortality more accurately than office measurements precisely because it represents a large sample of readings taken under consistent conditions. 1, 4

For stable, controlled patients, repeat this 7-day monitoring protocol every 3 months; during medication titration, repeat after 2-4 weeks. 2