An economic evaluation of using a clinical decision rule (PROOF-BP) in the diagnosis of hypertension in Primary Care
Clinical guidelines in England suggest that individuals presenting in Primary Care with a clinic blood pressure (BP) reading of 140/90mmHg or above (suspected hypertension) should have ambulatory blood pressure monitoring (ABPM) for confirmatory diagnosis. This excludes people with normal clinic blood pressure which is raised on ABPM (masked hypertension) despite evidence to suggest that this is common – 10-15% – and that such individuals are at an increased risk of cardiovascular disease (similar to overt hypertension). Conversely, patients with raised clinic blood pressure which is normal on ABPM (white-coat hypertension) needlessly incur the high expense of ABPM. The PRedicting Out-of-Office Blood Pressure (PROOF-BP) risk algorithm uses patient characteristics and multiple clinic BP measurements to predict masked, white-coat and sustained hypertension. The PROOF-BP algorithm gives either definitive diagnosis (of hypertension or normotension) or suggests further investigation (i.e. ABPM), thus reducing inappropriate treatment and increasing the chance of identification of masked and sustained hypertension. This study assessed the cost effectiveness of using this clinical decision rule for targeting patients for ABPM in the diagnosis of hypertension in Primary Care.
A cost-utility model previously developed for National Institute for Health and Care Excellence (NICE) hypertension guidelines was adapted to accommodate the PROOF-BP diagnostic strategy and a broader patient population (including people with apparently normotension on initial clinic measurement). Modelling adopted a lifetime horizon with a National Health Service perspective. Strategies for BP diagnosis comprised clinic blood pressure monitoring, home blood pressure monitoring, PROOF-BP or ABPM. Results for each strategy were presented in terms of cost per Quality Adjusted Life Year (QALY) gained compared to next best alternative comparator.
The PROOF-BP risk algorithm was cost-effective in the base-case model population (all patients with clinic BP ≥130/80mmHg) and widened model population (all patients with clinic BP ≥120/70mmHg) for all age and gender groups if decision makers were willing to pay up to £20,000/QALY gained, when compared with ABPM only for patients with a clinic BP of ≥140/90mmHg. 14,623 additional people with hypertension would be detected per 100,000 screening population and 9,548 additional cardiovascular events would be prevented compared to current recommendations. Deterministic and probabilistic sensitivity analyses supported the base case findings. Results were most sensitive to assuming a quality of life decrement associated with antihypertensive treatment.
This is the first analysis to examine the cost-effectiveness of targeted use of ABPM in the diagnosis of hypertension. The PROOF-BP risk algorithm appears to be cost-effective compared to the conventional BP diagnostic options in Primary Care and would lead to reduced death and disability. Limitations of the model include the lack of data on the assumed efficacy of antihypertensive treatment for masked hypertension and assumptions regarding the true prevalence of masked hypertension.