Treatment cut-offs for blood pressure lowering and lipid lowering treatment: a cohort study in UK primary care

Date of ISAC Approval: 
19/06/2019
Lay Summary: 
In the UK, blood pressure guidelines recommend use of blood pressure drugs for all patients with blood pressures of 160/100mmHg and above. However, the reason that this cut off has been chosen is unclear, since there is no sudden increase in the risk of heart attacks and strokes above this level. Treating high blood pressure also reduces the risk of damage to organs including the kidney, heart, eye and brain, but it is unclear at which level of blood pressure the risk of this damage increases. Similarly, UK guidelines for lipid lowering drugs (statins) recommend referral to specialist doctors when cholesterol levels reach a certain cut-off (9mmol/litre for total cholesterol). The reason for this choice of cut-off is unclear. Crucially, among thousands of people in the UK, these cut-offs determine whether or not people receive drugs and additional care that could reduce their risk of heart attacks and strokes. Making decisions about which patients to treat should be guided by evidence. Therefore this study investigates whether there are cut-offs, for either blood pressure or cholesterol, above which treatment would be more beneficial. We will use data from UK primary care, and group patients according to their level of blood pressure, cholesterol, and their predicted risk of disease. We will then see which patients go on to have heart attacks, strokes and damage to their kidney, heart, eye and brain. By comparing groups, we will be able to see which groups would benefit most from treatment.
Technical Summary: 
In the UK, blood pressure guidelines recommend use of blood pressure lowering drugs for patients with blood pressures of 160/100mmHg and above, irrespective of their absolute cardiovascular disease risk. However, there is little evidence to justify this cut-off because the relationship between blood pressure and CVD events is log linear. Similarly, NICE guidelines for lipid lowering drugs (statins) recommend specialist investigation when total cholesterol is 9mmol/L, or non-HDL cholesterol is above 7.5mmol/L, irrespective of absolute cardiovascular disease risk. As with blood pressure, the evidence base for these cut-offs is unclear. Crucially, among thousands of people in the UK, the blood pressure cut-off determines eligibility for drugs that can reduce the risk of cardiovascular disease by 20%, and cholesterol cut-offs determine whether further health care is provided. Making decisions about which patients to treat should be guided by evidence. Therefore this study aims to determine whether there are levels of either blood pressure or cholesterol above which treatment is justified. Using data from UK primary care, we will generate a cohort of patients without cardiovascular disease, and stratify them by their predicted absolute cardiovascular disease risk, blood pressure and cholesterol at cohort entry. We will follow them up and observe the rate of cardiovascular disease and target organ damage in each stratum. This will provide evidence about whether there should be cut offs at which treatment or further investigation are warranted, irrespective of risk.
Health Outcomes to be Measured: 
Cardiovascular disease (coronary heart disease, cerebrovascular disease, peripheral arterial disease, heart failure) Target organ damage: chronic kidney disease, left ventricular hypertrophy, hypertensive retinopathy, dementia.
Collaborators: 

Rod Jackson - Chief Investigator - University of Auckland
Dr Emily Herrett - Corresponding Applicant - London School of Hygiene & Tropical Medicine (LSHTM)
Professor Liam Smeeth - Collaborator - London School of Hygiene & Tropical Medicine (LSHTM)

Linkages: 
HES Admitted;ONS;Patient Townsend;Pregnancy Register