Comparison of agreement between different measures of blood pressure in primary care and daytime ambulatory blood pressure

doi:10.1136/bmj.325.7358.254

BMJ 2002;325:254 ( 3 August )

Primary care

Comparison of agreement between different measures of blood pressure in primary care and daytime ambulatory blood pressure

Paul Little, MRC clinician scientist, ^a Jane Barnett, research nurse, ^a Lucy Barnsley, medical student, ^a Jean Marjoram, practice nurse, ^b Alex Fitzgerald-Barron, general practitioner, ^c David Mant, professor. ^a

^aCommunity Clinical Sciences Division (Primary Medical Care Group), Faculty of Medicine, Health and Biological Sciences, Southampton University, Aldermoor Health Centre, Southampton SO16 5ST, ^b Nightingale Surgery, Greatwell Drive, Romsey SO51 7QN, ^c St Clements Surgery, Winchester SO23 8AD

Correspondence to: P Little psl3{at}soton.ac.uk

Primary care p 258

Objective: To assess alternatives to measuring ambulatorypressure, which best predicts response to treatment and adverseoutcome.
Setting: Three general practices inEngland.
Design: Validationstudy.
Participants: Patients with newly diagnosed high or borderlinehigh blood pressure; patients receiving treatment for hypertensionbut with poorcontrol.
Main outcome measures: Overall agreement with ambulatory pressure;prediction of high ambulatory pressure (>135/85 mm Hg) and treatmentthresholds.
Results: Readings made by doctors were much higherthan ambulatory systolic pressure (difference 18.9 mm Hg, 95%confidence interval 16.1 to 21.7), as were recent readings madein the clinic outside research settings (19.9 mm Hg,17.6 to 22.1).This applied equally to treated patients with poor control (doctorv ambulatory 21.4 mm Hg, 17.3 to 25.4). Doctors' and recent clinicreadings ranked systolic pressure poorly compared with ambulatorypressure and other measurements (doctor r=0.46; clinic 0.47; repeatedreadings by nurse 0.60; repeated self measurement 0.73; home readings0.75) and were not specific at predicting high blood pressure(doctor 26%; recent clinic 15%; nurse 72%; patient in surgery81%; home 60%), with poor likelihood ratios for a positive test(doctor 1.2; clinic 1.1; nurse 2.1, patient in surgery 4.7; home2.2). Nor were doctor or recent clinic measures specific in predictingtreatmentthresholds.
Conclusion: The "white coat" effect is important in diagnosingand assessing control of hypertension in primary care and is nota research artefact. If ambulatory or home measurements are notavailable, repeated measurements by the nurse or patient shouldresult in considerably less unnecessary monitoring, initiation,or changing of treatment. It is time to stop using high bloodpressure readings documented by general practitioners to maketreatmentdecisions.

What is already known on this topic
Prospective studies indicate that ambulatory blood pressure is a much better predictor of adverse outcome and response to treatment than readings made by a doctor

Preliminary evidence suggests that measurements by doctors are likely to be higher than those made by nurses, technicians, or patients

No study has compared all the available measures in a typical primary care setting with ambulatory blood pressure in patients with newly diagnosed and established hypertension

What this study adds
The white coat effect associated with measurements by doctors is not an artefact of research studies; it applies equally in primary care and for both initial diagnosis and assessment of control

If ambulatory measurement is not possible, repeated measurement by a nurse or by the patient will result in much less unnecessary treatment or change in treatment for high blood pressure

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