Age-dependent changes in blood pressure over consecutive office measurements: impact on hypertension diagnosis and implications for international guidelines

Objectives: Based on anecdotal belief that blood pressure (BP) drops over consecutive measurements, guidelines recommend discarding the first BP reading (Canadian Hypertension Education Program guidelines) or take only one reading if SBP less than 140 mmHg (National Institute for Health and Care Excellence). However, the extent to which SBP fluctuations affect BP classification as well as the potential effect of age are unknown. We sought to assess the change in SBP classification over consecutive measurements following different guidelines, among younger (< 50 years) and older individuals (≥ 50 years). Furthermore, we aimed to investigate the direction of the change in SBP over consecutive measurements (increase or decrease) and the impact of age on SBP differences.

Methods: BP was measured among 20 716 adults from a general population. SBP was classified using the first reading (normal SBP or hypertension) and compared with the average SBP using different guideline protocols (reclassification).

Results: Reclassification from normal SBP to hypertension was greatest with Canadian Hypertension Education Program guidelines (3% younger, 12% older individuals) and reclassification from hypertension to normal SBP was greatest with National Institute for Health and Care Excellence guidelines (70% younger, 44% older individuals). SBP increased between the first two measures in 37%, decreased in 56% and did not change in 7% of the population. Age had a strong interaction with SBP level (P <  0.0001) so that younger individuals exhibited greater SBP differences over repeated measures.

Conclusion: This study highlights the need for an improvement in the evidence-base regarding the best way to assess office BP for correct hypertension diagnosis.