General Practice

Using thresholds based on risk of cardiovascular disease to target treatment for hypertension: modelling events averted and number treated

Simon Baker, registrar in public health medicine, ^a Patricia Priest, Nuffield fellow, ^b Rod Jackson, professor of epidemiology. ^c

^a Health Funding Authority, Private Bag 92522, Wellesley St, Auckland, New Zealand, ^b Wolfson College, Oxford OX2 6UD, ^c Department of Community Health, Faculty of Medical and Health Science, University of Auckland, Private Bag 92019, Auckland, New Zealand

Correspondence to: R Jackson rt.jackson{at}auckland.co.nz

Objective: To estimate the impact of using thresholds based on absolute risk of cardiovascular disease to target drug treatment to lower blood pressure in the community.
Design: Modelling of three thresholds of treatment for hypertension based on the absolute risk of cardiovascular disease. 5 year risk of disease was estimated for each participant using an equation to predict risk. Net predicted impact of the thresholds on the number of people treated and the number of disease events averted over 5 years was calculated assuming a relative treatment benefit of one quarter.
Setting: Auckland, New Zealand.
Participants: 2158 men and women aged 35-79 years randomly sampled from the general electoral rolls.
Main outcome measures: Predicted 5 year risk of cardiovascular disease event, estimated number of people for whom treatment would be recommended, and disease events averted over 5 years at different treatment thresholds.
Results: 46 374 (12%) Auckland residents aged 35-79 receive drug treatment to lower their blood pressure, averting an estimated 1689 disease events over 5 years. Restricting treatment to individuals with blood pressure 170/100 mm Hg and those with blood pressure between 150/90-169/99 mm Hg who have a predicted 5 year risk of disease 10% would increase the net number for whom treatment would be recommended by 19 401. This 42% relative increase is predicted to avert 1139/1689 (68%) additional disease events overall over 5 years compared with current treatment. If the threshold for 5 year risk of disease is set at 15% the number recommended for treatment increases by <10% but about 620/1689 (37%) additional events can be averted. A 20% threshold decreases the net number of patients recommended for treatment by about 10% but averts 204/1689 (12%) more disease events than current treatment.
Conclusions: Implementing treatment guidelines that use treatment thresholds based on absolute risk could significantly improve the efficiency of drug treatment to lower blood pressure in primary care.