A modelling study suggests that ambulatory blood pressure (BP) monitoring to diagnose hypertension in patients who have a high BP on screening is more cost effective than further clinic measurements or home measurement.

The authors of this study, co-sponsored by NICE, note that hypertension is traditionally diagnosed following several raised BP measurements in the clinic; however they note that home monitoring and particularly ambulatory monitoring correlate better with adverse clinical outcomes and may be preferable for diagnosis. Such a strategy would, however, require substantial investment in equipment. This model was developed, therefore, to determine the cost-effectiveness of ambulatory and home BP monitoring for diagnosis of hypertension compared to further blood pressure measurement in the clinic, in patients found to have a raised BP on screening in clinic. The analysis was carried out using a Markov model based on a hypothetical primary care population of adults aged over 40 with a screening BP measurement over 140/90 mmHg. Strategies compared were three further BP measurements in the clinic at monthly intervals, measurement over one week at home, and 24 hours measurement with an ambulatory monitor. Outcomes were costs, Quality Adjusted Life Year (QALY), and incremental cost per QALY, using current UK NHS and personal social services perspective.

The model found ambulatory monitoring to be the most cost-effective strategy for diagnosis of hypertension in all patient groups studied; it was cost-saving in all, and it increased QALY in all groups aged 50 and over. Most of the savings came from avoiding treatment in patients who would not be considered hypertensive, due the greater specificity of the method. Although the incremental cost of diagnosis was higher (£42; 95% CI, £22 to £57)), the discounted treatment costs were lower and the costs of subsequent events were similar.

The model was robust to a wide range of sensitivity analyses. In these, only two scenarios changed the overall results: if home monitoring was as effective as ambulatory monitoring it became more cost-effective due to its lower cost, and if treatment of people who were falsely diagnosed as hypertensive reduced adverse outcomes then clinic measurement became more cost-effective because more people would be treated and QALY would increase.

Based on the results of the model, the authors conclude that ambulatory monitoring was most cost-effective for confirming a diagnosis of hypertension after an initial high reading in the clinic. It would reduce misdiagnosis and thus reduce the number of people being treated, with consequent cost saving. The results were robust to most sensitivity analyses, with the only two exceptions: either that home monitoring was as effective, which is disputed by recent evidence, and if treatment of people not needing it gave benefit but no harms.

An accompanying Comment discusses the study. The author notes the strengths of the analysis, but comments on some nuances. He notes that more frequent screening reduced the cost saving with ambulatory monitoring, although it might still be cost-effective, and suggests that frequency might be better based on overall risk. He also notes that recent guidelines recommend treatment based on absolute risk – as people with hypertension tend to have other risk factors this probably strengthens the results, however this aspect should be tested.

[Editor’s note: NICE has already revised its guideline on hypertension based on the results of this analysis.]