Differences in clinic and ambulatory measurements of blood pressure: Diagnostic and treatment thresholds defined
Hypertension is a major contributor to the burden of illness in Australia and non-optimal blood pressure is the third major cause of total disease burden (DALYS). In general practice, high blood pressure accounted for 18.5% of all chronic problems. Blood pressure measurements taken in the clinic or physician’s office provide limited information about the true blood pressure load, and home or ambulatory measurements are often needed to best guide the diagnosis and treatment of hypertension. Ambulatory blood pressure monitoring more accurately reflects a patient’s blood pressure and correlates more closely with end-organ complications than blood pressure levels measured in the physician’s office.
Published last week in the highly accredited British Medical Journal, is the prospective Australian study (1) which has derived reference ambulatory blood pressure thresholds for the diagnosis and management of hypertension that accounted for age and sex. Dr Anastasia Susie Mihailidou from Royal North Shore Hospital & Sydney Medical School along with colleagues from Southwestern Area Health Service and the Baker Research Institute, initiated this national multicentre study, which included the Ambulatory Blood Pressure Working Group of the High Blood Pressure Research Council of Australia.
The research is part of a joint initiative between the High Blood Pressure Research Council of Australia and the National Heart Foundation of Australia, which aims to support appropriate use and interpretation of ambulatory blood pressure monitoring and effective management of blood pressure in the primary care setting. As indicated in the article:
WHAT IS ALREADY KNOWN
Several prospective controlled studies have shown ambulatory blood pressure predicts cardiovascular outcome better than clinic blood pressure, with defined equivalent thresholds for diagnosis of mild hypertension. Guidelines for the management of hypertension in patients with pre-existing cardiovascular disease or risk factors suggest that target values should be different from those in patients without such factors, but ambulatory equivalents have not been defined. Blood pressure measured in the clinic by physicians more often is higher than that measured by other trained professional staff – the “white coat” effect.
WHAT THIS STUDY ADDS
Regression analysis showed that the hypertension thresholds and target values for daytime ambulatory blood pressure were slightly lower than the equivalent clinic values. Ambulatory values were 1/2 mm Hg lower for women than for men and 3/1 mm Hg lower in older people (65 years and older) than in younger people. Doctors’ measurements of clinic blood pressure were higher than those of trained staff and therefore are inappropriate for estimation of ambulatory blood pressure treatment thresholds. Review of the reference ambulatory blood pressure equivalents used for management of hypertension is recommended.
(1) Head G, Mihailidou AS, Duggan K, Beilin LJ, Berry N, Brown MA, Bune A, Cowley D, Chalmers JP, Howe PRC, Hodgson J, Ludbrook J, Mangoni AA, McGrath BP, Morley CM, Nelson MR, Sharman JE, Stowasser M. (BMJ 2010;340:c1104, Online)
Relationship between ambulatory and Clinic Blood Pressure: Defining diagnostic and treatment targets.