Daytime ambulatory lower than clinic BP diagnostic thresholds
MedWire News: Daytime ambulatory blood pressure (BP) thresholds are slightly lower than equivalent clinic values for diagnosis and treatment of hypertension, Australian researchers report in the British Medical Journal.
They found ambulatory BP values were between 2/2 mmHg and 12/6 mmHg lower than the upper limits of clinic BP used to diagnose normal BP and mild, moderate, and severe hypertension. The closer to normal BP, the greater the agreement was between ambulatory and clinic BP measures.
Authors Geoffrey Head (Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia) and colleagues suggest that guidelines “can include the thresholds identified in the current study to guide management of hypertension.”
The team analyzed 24-hour ambulatory BP data for 8529 patients from 11 centers across Australia. The patients’ average age was 56 years and their average body mass index was 28.9 kg/m2. A large proportion (69%) were receiving medications for hypertension and most were White.
Using regression analysis to determine the relationship between ambulatory and clinic BP measurements, the researchers found that the patients’ daytime systolic/diastolic ambulatory BP equivalent to the lower limit of grade 1 or mild hypertension was 4/3 mmHg lower than the standard seated clinic BP value of 140/90 mmHg, at 136/87 mmHg.
The estimated daytime ambulatory BP for grade 2 or moderate hypertension was 8/4 mmHg lower than the standard of 160/100 mmHg, and that for grade 3 or severe hypertension was 12/6 mmHg lower than the usual clinic BP threshold of 180/110 mmHg.
In addition, the daytime ambulatory BP equivalent was 2/2 mmHg lower than the clinic BP threshold of 130/80 mmHg for patients with associated conditions and 1/1 mmHg lower than the upper limit of 125/75 mmHg for normal BP.
Furthermore, equivalents were 1/2 mmHg lower for women than for men, and 3/1 mmHg lower in the elderly aged 65 years or older than in younger people.
Richard McManus (University of Birmingham, UK) discussed the study’s relevance to clinical practice in an accompanying editorial, noting that antihypertensive treatments have an extensive base derived from measurement of clinic BP.
“Clinicians faced with divergent clinic and ambulatory measurements will still be unsure which method of monitoring and what thresholds and targets are most appropriate for clinical decision making,” he commented.
One solution is to concentrate on cardiovascular risk, an approach gradually being adopted in management guidelines.
“Follow-up of this cohort would provide an opportunity for additional analysis to allow results of ambulatory BP monitoring to be included in risk calculators,” said McManus.
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By Caroline Price