Optimal number of days for home blood pressure measurement.
BACKGROUND
Current guidelines make no outcome-based recommendations on the optimal measurement schedule for home blood pressure (BP).


METHODS
We enrolled 4,802 randomly recruited participants from three populations. The participants were classified by their (i) cross-classification according to office and home BP (normotension, masked hypertension, white-coat hypertension, and sustained hypertension) and (ii) home BP level (normal BP, high normal BP, grade 1 and 2 hypertension), while the number of home measurement days was increased from 1 to 7. The prognostic accuracy of home BP with an increasing number of home BP measurement days was also assessed by multivariable-adjusted Cox models.


RESULTS
Agreement in classification between consecutive measurement days indicated near perfect agreement (κ ≥ 0.9) after the sixth measurement day for both office and home BP cross-classification (97.8% maintained classification, κ = 0.97) and home BP level (93.6% maintained classification, κ = 0.91). Over a follow-up of 8.3 years, 568 participants experienced a cardiovascular event, and the first home BP measurement alone predicted events significantly (P ≤ 0.003). The confidence intervals (CIs) were too wide and overlapping to show superiority of multiple measurement days over the first measurement day (hazard ratios per 10mm Hg increase in systolic BP at initial day, 1.11 [CI 1.07-1.16]; that at 1-7 days, 1.18 [CI 1.12-1.24]). Masked hypertension, but not white-coat hypertension, was associated with increased cardiovascular risk, irrespective of the number of home measurement days.


CONCLUSIONS
Even a single home BP measurement is a potent predictor of cardiovascular events, whereas seven home measurement days may be needed to reliably diagnose hypertension.
Population Studies Unit, Department of Chronic Disease Prevention, National Institute for Health and Welfare, Turku, Finland; Department of Medicine, Turku University Hospital, Turku, Finland;
Teemu J
TJ
Niiranen
Department of Planning for Drug Development and Clinical Evaluation, Tohoku University Graduate School of Pharmaceutical Sciences, Sendai, Japan; Department of Hygiene and Public Health, Teikyo University School of Medicine, Tokyo, Japan;
Kei
K
Asayama
Studies Coordinating Centre, Research Unit Hypertension and Cardiovascular Epidemiology, KU Leuven Department of Cardiovascular Sciences, University of Leuven, Leuven, Belgium;
Lutgarde
L
Thijs
Population Studies Unit, Department of Chronic Disease Prevention, National Institute for Health and Welfare, Turku, Finland;
Jouni K
JK
Johansson
Studies Coordinating Centre, Research Unit Hypertension and Cardiovascular Epidemiology, KU Leuven Department of Cardiovascular Sciences, University of Leuven, Leuven, Belgium;
Azusa
A
Hara
Department of Preventive Medicine and Epidemiology, Tohoku Medical Megabank Organization, Tohoku University, Sendai, Japan;
Atsushi
A
Hozawa
Department of Public Health, Tohoku University Graduate School of Medicine, Sendai, Japan;
Ichiro
I
Tsuji
Department of Planning for Drug Development and Clinical Evaluation, Tohoku University Graduate School of Pharmaceutical Sciences, Sendai, Japan; Department of Hygiene and Public Health, Teikyo University School of Medicine, Tokyo, Japan;
Takayoshi
T
Ohkubo
Population Studies Unit, Department of Chronic Disease Prevention, National Institute for Health and Welfare, Turku, Finland;
Antti M
AM
Jula
Department of Planning for Drug Development and Clinical Evaluation, Tohoku University Graduate School of Pharmaceutical Sciences, Sendai, Japan;
Yutaka
Y
Imai
Studies Coordinating Centre, Research Unit Hypertension and Cardiovascular Epidemiology, KU Leuven Department of Cardiovascular Sciences, University of Leuven, Leuven, Belgium; VitaK Research and Development, Maastricht University, Maastricht, The Netherlands. jan.staessen@med.kuleuven.be ja.staessen@maastrichtuniversity.nl.
Jan A
JA
Staessen
D000368:Aged; D001794:Blood Pressure / Q000502:physiology*; D018660:Blood Pressure Monitoring, Ambulatory / Q000379:methods*; D002940:Circadian Rhythm; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D059468:Masked Hypertension / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D008875:Middle Aged; D011379:Prognosis; D011446:Prospective Studies
blood pressure; cardiovascular diseases; home blood pressure monitoring; hypertension; meta-analysis; prognosis.