First Blood Pressure Reading Elevation: Physiology and Measurement Guidelines

Physiological Basis

The first day's readings should be discarded because they are systematically higher and less reliable than subsequent measurements, reducing the accuracy of blood pressure assessment and potentially leading to overdiagnosis of hypertension 4, 5, 6, 7

The American Heart Association, American Society of Hypertension, and Preventive Cardiovascular Nurses Association jointly recommend following European Society of Hypertension guidelines: take at least 2 morning and 2 evening readings daily for 1 week, but discard the first day's readings, yielding 12 total readings for clinical decisions 8, 9, 10, 11
Patients should measure BP twice daily (morning before medications and evening) for 7 consecutive days, with 2 readings at each session separated by 1 minute 8, 9, 10, 11
After excluding the first day, this provides 12 readings (6 days × 2 sessions per day) on which to base clinical decisions 8, 9, 10, 11

Including first-day readings increases the risk of misclassifying patients as hypertensive when they have white coat hypertension or normal BP 4, 5, 6, 7
Home BP monitoring already tends to be lower than office BP due to absence of the white coat effect; proper technique including discarding day 1 ensures the most accurate assessment 8, 9
Patients should be instructed to record all readings they take, but clinicians should calculate the average using only days 2-7 8, 9, 10, 11
Using devices with memory storage is encouraged to ensure accurate reporting and prevent patients from selectively reporting lower readings 8, 9

Hypertension, 2008

Hypertension, 2008