BpTRUth: do automated blood pressure monitors outperform mercury?

Manual measurement of blood pressure (BP) in the office (MOBP) is inferior in accuracy when compared with ambulatory BP measurements (ABPM) since it misses white coat and masked effects on BP. BpTRU, an automated office BP device (AOBP), has been reported to reduce white coat effect. We performed a retrospective review of the diagnostic accuracy of MOBP (taken by a trained nurse in clinical hypertension) and AOBP using the Bland-Altman method in hypertensive patients referred to a Renal Hypertension Clinic. In 329 hypertensive patients, the 95% limits of agreement between systolic AOBP and ABPM were -31 mm Hg to 33 mm Hg and for MOBP and ABPM were -27.8 mm Hg to 37.4 mm Hg. The bias between systolic MOBP and systolic ABPM was 4.9 mm Hg (95% confidence interval, 3.0-6.6 mm Hg) whereas the bias between the systolic AOBP and the systolic ABPM was -3.2 (95% confidence interval, -1.3 to -5.0). AOBP did not improve treatment relevant classification errors compared with MOBP (28% vs. 23%; P = .052). Our data support findings by others showing that AOBP improves, but does not eliminate, white coat effect. The increased detection of white coat effect appears related to systematic downward bias by BpTRU. As a result, detection of masked effect is undermined by BpTRU.