Published 30 April 2009, doi:10.1136/bmj.b1492
Cite this as: BMJ 2009;338:b1492

Research

Long term monitoring in patients receiving treatment to lower blood pressure: analysis of data from placebo controlled randomised controlled trial

¹ Screening and Test Evaluation Program (STEP), School of Public Health, Building A27, University of Sydney, New South Wales 2006, Australia, ² George Institute for International Health, Royal Prince Alfred Hospital, Building C39, University of Sydney, New South Wales

Objective To determine the value of monitoring blood pressure by quantifying the probability that observed changes in blood pressure reflect true changes.

Design Analysis of blood pressure measurements of patients in the perindopril protection against recurrent stroke study (PROGRESS).

Setting Randomised placebo controlled trial carried out in 172 centres in Asia, Australasia, and Europe.

Participants 1709 patients with history of stroke or transient ischaemic attack randomised to fixed doses of perindopril and indapamide.

Measurements Mean of two blood pressure measurements in patients receiving treatment recorded to the nearest 2 mm Hg with a standard mercury sphygmomanometer at baseline and then at three months, six months, nine months, and 15 months and then every six months to 33 months.

Results There was no change in the mean blood pressure of the cohort during the 33 month follow-up. Six months after blood pressure was stabilised on treatment, if systolic blood pressure was measured as having increased by >10 mm Hg, six of those measurements would be false positives for every true increase of 10 mm Hg. The corresponding value for an increase of 20 mm Hg was over 200. Values for 5 mm Hg and 10 mm Hg increases in diastolic blood pressure were 3.5 and 39, respectively. The likelihood that observed increases in blood pressure reflected true increases rose with the time between measurements such that the ratio of true positives to false positives reached parity at 21 months.

Conclusions Usual clinical approaches to the monitoring of patients taking drugs to lower blood pressure have a low probability of yielding reliable information about true changes in blood pressure. Evidence based guidelines for monitoring treatment response are urgently required to guide clinical practice.

Trial registration Australia and New Zealand Clinical Trial Registry.

© Keenan et al 2009
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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