Does the higher or lower reading arm best reflect systolic blood pressure? An individual participant data meta-analysis from the INTERPRESS-IPD Collaboration
Hypertension guidelines recommend measuring blood pressure (BP) in both arms, adopting the higher arm readings for diagnosis and management. To our knowledge, no publications justify these recommendations – they are currently based on expert consensus advice. We have previously found that this guidance is not always adhered to, and that a minority of practitioners adopt the lower reading arm for diagnosis and management . We therefore aimed to evaluate the impact of using higher or lower arms systolic BPs on prognosis and treatment decisions.
Individual participant data meta-analyses: Using data in the Inter-arm Blood Pressure Difference Collaboration (INTERPRESS-IPD) pooled from 23 cohorts we examined associations between higher and lower reading arm BPs and event outcomes using multivariable Cox regression models stratified by study. Models using higher and lower arm BPs were compared and prediction of events based on Framingham, Atherosclerotic Cardiovascular Disease (ASCVD) and Systematic COronary Risk Evaluation (SCORE) risk scores was calculated from either higher or lower arm BPs. Proportions of participants reclassified across guideline recommended BP and cardiovascular risk treatment thresholds were explored.
Bilateral BP measurements existed for 53,172 participants: mean age 60 years; 48% female. Higher arm BP better predicted all-cause mortality, cardiovascular mortality, and cardiovascular events compared to lower arm BP (P<0.001 all outcomes). For participants without cardiovascular disease, higher arm BP better predicted cardiovascular events using Framingham (N=23,278) or ASCVD (N=18,557) risk scores compared to lower arm BP (P<0.001 for both). No difference was observed for models based on SCORE (N=18,017), however, switching from lower arm to higher arm BP reclassified 4.6% , 3.5% and 7.7% of participants to a higher guideline-recommended risk category using the Framingham, ASCVD and SCORE models respectively. For guideline recommended BP treatment thresholds 12% were reclassified from below to above both 130 mmHg and 140 mmHg systolic thresholds (P<0.001 for all).
In this study more than one in ten people were recategorized to require additional treatment by using the BP from the higher reading arm in comparison to the lower arm; this significantly improved prognostic ability. Both arms should be measured during assessment and the higher arm BP adopted for diagnosis and management of hypertension. These findings provide the first empirical evidence in support of these guideline recommendation.