Interarm blood pressure measurement and the reference-arm assignment variability

Abstract

The arm with the higher blood pressure (BP) is assigned as the follow up arm for hypertensive patients (reference-arm). We evaluated the reproducibility of this assignment. BP was measured simultaneously on both arms with a double cuff validated device in two visits separated <10 days (two sets of three readings per visit). Two reference-arms were assigned in each visit (the arm with higher BP, at least ≥1 mmHg). The intravisit and intervisit agreements of this assignment were evaluated. We included 313 hypertensive patients. First visit mean right arm BP was 131.6 (16.6)/75.3 (9.4) mmHg and left arm BP was 132.4 (16.9)/75.7 (9.7) mmHg (P = 0.002). Intravisit concordance at the first and second visits were κ = 0.60 [95% confidence interval (CI), 0.516-0.696] and κ = 0.45 [95% CI, 0.356-0.555], respectively. Therefore, 21.8% of patients (at the first visit) and 29.1% (at the second visit) with the right arm as the reference-arm in the first round of readings changed to the left arm in the same visit in the second round of readings. The intervisit κ index was 0.25 [95% CI, 0.147-0.365]. After that, 36.8% of patients with the right arm as the reference-arm at the first visit changed to the left arm at the second visit. The subgroup (9.5%) with an interarm systolic BP difference ≥10 mmHg at the first visit did not differ significantly from the rest of patients. The reference-arm assignment agreement is weak to moderate. The assignment of the reference-arm should be individualized and not considered as definitive.