Australian researchers calculated the average of two BP readings taken at baseline and at three, six, nine, 15, 21, 27 and 33 months.
Readings were measured for 1,709 patients on fixed doses of an ACE-inhibitor and a thiazide diuretic. There was no change in the mean BP of the patient cohort over the whole follow-up period.
The researchers calculated that, because of variations in measurement, for every seven patients measured as having a 10 mmHg increase in systolic BP over six months, six measurements would be false positives.
Readings would have to be taken at least 21 months apart for a reading to be more likely to be a true positive than a false positive, they found.
'The probability of correctly identifying true increases in BP of moderate magnitude using a typical monitoring regimen is poor, with a large proportion of observed increases in BP being false positives,' they said.
'Clinicians need better information about the value of different monitoring strategies, and future evidence-based monitoring guidelines would be invaluable,' they conclude.
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