The rationale for the use of ambulatory blood pressure monitoring (ABPM) has been the subject of critical reviews and published guidelines.1-6 Perhaps the most important and challenging finding to emerge from ambulatory blood pressure research has been the detection of "white coat" hypertension (also known as isolated clinic hypertension) in about 20% of subjects with repeatedly elevated casual blood pressure readings taken in the doctor's clinic.7,8 The condition can only be detected by ABPM or self-monitoring, and there are no specific predisposing factors. For people with white coat hypertension and no evidence of cardiovascular disease or comorbidities such as diabetes or renal disease, most experts agree that the best policy is to monitor their clinic blood pressure regularly, with self-monitoring at home, and repeat ABPM at one- to two-yearly intervals.

The importance of continued monitoring is borne out by the evidence now emerging that white coat hypertension may not be an entirely innocent phenomenon.5,6 The initial studies that examined the cost savings in the detection of white coat hypertension by ABPM7,8 did not consider the need for long-term surveillance and the conversion of patients with white coat hypertension to established hypertension; this might be as high as 75% over six years of follow-up.9 The development of hypertension on ABPM criteria could not be predicted by changes in clinic blood pressures.

The cost-analysis study of ABPM in Australian general practice reported by Ewald and Perkarsky in this issue of the Journal (page 580)10 is important for a number of reasons. The study confirms the high prevalence of white coat hypertension previously reported in the Australian community,11 and reflects current general practice, because GPs decided on the basis of conventional clinic readings that drug treatment was indicated before ordering ABPM.

This cost analysis is the first such study based on Australian data, including best estimates of current pharmacological management of hypertension in Australia. It has also factored in a 10% per year conversion rate from white coat hypertension to established hypertension. The sensitivity analysis showed that all monitoring strategies (ABPM at 1-, 2-, or 3-year intervals) were less expensive than no monitoring over a projected seven-year period.

The study almost certainly underestimated the average costs of investigations of hypertension, including standard investigations, documentation of target-organ effects and specific investigations in selected subjects to exclude secondary hypertension. The potential costs of adverse drug reactions were not considered. However, both of these would amplify the difference towards greater cost saving with the use of ABPM. Another important attributable cost is that of the perception of unwellness that accompanies inappropriate labelling as "hypertensive", which can lead to loss of productivity, sick leave, anxiety and the development of symptoms.

There are other groups of patients in whom ABPM might have cost-saving benefits. Staessen et al12 reported on a study in 419 patients randomised to be treated according to their daytime ambulatory blood pressure or their clinic blood pressure, with the latter group receiving usual care. The mean follow-up was six months, and the two groups had similar mean left ventricular mass at the end of the study. The ambulatory blood pressure group had a 19% decrease in antihypertensive drug use and an 11% fall in doctors' fees. Some treated hypertensive patients exhibit a marked difference between ambulatory blood pressure and clinic blood pressure, and assessment of the effectiveness of antihypertensive therapy using clinic blood pressure readings tends to overestimate responses to drug therapy by including the "placebo" component of the reduction in blood pressure, which is minimal with ABPM. The results of the Syst-Eur study of systolic hypertension show that conventional clinic blood pressure measurements lead to an overestimate of the prevalence of isolated systolic hypertension among elderly patients.13 This suggests the potential for excessive treatment and associated complications in a significant proportion of elderly patients. This white coat effect is reproducible.14 The recognition of white coat hypertension in pregnancy, which may occur in as much as 30% of pregnancies,15 has the potential to reduce anxiety, hospital admissions and drug use, with significant cost savings.

Some notes of caution are warranted. A major one is that we still await the results of definitive outcome studies in controlled trials comparing management of hypertension based on clinic blood pressure versus ambulatory blood pressure. The technique of ABPM is specialised, and service providers must use validated monitors and quality control measures. Current provision of ABPM is not regulated in Australia and is not recognised through the Medical Benefits Scheme. Another cautionary note is that all available evidence suggests that hypertension in our community is more undertreated than overtreated.

The use of self-monitoring is also increasing, although there are more concerns with self-recording devices. In a recent analysis,16 only five of 23 devices met acceptable criteria. A combination of the two has a lot to offer: ABPM may be better for the initial diagnosis of hypertension and for predicting prognosis, while self-monitoring may be of more value for the long-term follow-up of patients.

ABPM is an important diagnostic tool in the management of hypertension. The study by Ewald and Perkarsky indicates that appropriate use can be of cost benefit to the Australian community.