Hypertension detection and cardiovascular outcomes: a retrospective cohort study using data from the Clinical Practice Research Datalink database

Date of ISAC Approval: 
15/05/2019
Lay Summary: 
Hypertension is when blood pressure (a measure of the force used to pump blood around the body) is persistently higher than the normal range of values. Individuals with hypertension are at increased risk of dying earlier due to cardiovascular disease (diseases of the heart or blood vessels), especially if not diagnosed, monitored and treated. However, if these patients receive the correct treatment, this risk is reduced. Not all patients who have had a high blood pressure reading have been followed up or diagnosed with hypertension on their medical records. This study will look at the differences in rates of death and cardiovascular disease in patients who have a diagnosis of hypertension in their medical records and those who do not. To do this we will look at the records of patients who had a blood pressure reading between 1st January 2006 and 31st December 2007, These patients will be divided into four groups based on: (1) whether that blood pressure reading was high or not (2) whether or not a diagnosis of hypertension is in their medical records, and (3) their raised blood pressure has been lowered. We will look at the numbers of patients in each group and differences in their characteristics (e.g. age, ethnicity), and then investigate if there is any difference in the rates of mortality and cardiovascular disease between the 4 groups. We hope this research will provide information on whether recording a diagnosis of hypertension in medical records leads to better health outcomes for patients.
Technical Summary: 
Hypertension is a common risk factor for cardiovascular mortality. It is the leading risk factor for premature death, stroke and heart disease worldwide (ref WHO 2012). It has been estimated that the global economic burden of increased blood pressure consumes US$370 billion worldwide and 10% of healthcare expenditures (ref Gaziano). Failure to detect hypertension influences mortality rates; higher proportions of the population on general practice hypertension registers are associated with lower premature mortality. However, a comparison of Quality and Outcomes Framework (QOF) hypertension registers and Health Survey for England (HSE) data indicates that a substantial proportion of patients with hypertension are not documented, and the literature for explaining this is limited. After adjusting for patient characteristics and other relevant factors, we will undertake Cox survival analysis to compare outcomes (mortality and incidence of cardiovascular disease ) between 4 cohorts of patients: a. Reference group (normal blood pressure and no prior read code for hypertension ) b. Raised blood pressure and no prior read code for hypertension c. Raised blood pressure and prior read code for hypertension d. Normal blood pressure and prior read code for hypertension By quantifying the current additional risks associated with raised blood pressure, we hope to inform local practices and policy makers in particular about the need to improve hypertension detection and control. In addition, if factors associated with failure to diagnose hypertension are identified (such as demographic characteristics including age, gender, or ethnicity), then, by sharing these findings with services, we anticipate that more patients not identified earlier can be added to hypertension registers and receive appropriate treatment within a 1 to 3-year time frame. In addition, we may identify factors for targeting patients by primary care teams to improve follow up until a diagnosis is made.
Health Outcomes to be Measured: 
The cohort will be divided into the following four groups: a. Reference group (normal blood pressure and no prior read code for hypertension) b. Raised blood pressure and no prior read code for hypertension c. Raised blood pressure and prior read code for hypertension d. Normal blood pressure and prior read code for hypertension Primary outcomes: Rates of all-cause and cardiovascular mortality and incidence of cardiovascular disease in the four cohorts Secondary outcomes: Description of baseline characteristics of the four groups Co-morbidities (diabetes mellitus, coronary or ischaemic heart disease, stroke, transient ischaemic attacks (TIA), peripheral arterial disease, obesity, chronic kidney disease) Lifestyle - Smoking status Demographic - Age - Gender - Ethnicity (subdivided into white, Afro-Caribbean, South Asian, other- including mixed) - Patient deprivation score (IMD 2015) - Prescriptions (numbers for British National Formulary code groups, e.g. blood pressure-lowering, lipid modification, diabetes) from previous year
Collaborators: 

Dr Louis Steven Levene - Chief Investigator - University of Leicester
Dr Francesco Zaccardi - Collaborator - University of Leicester
Miss Joanne Miksza - Collaborator - University of Leicester
Professor Kamlesh Khunti - Collaborator - University of Leicester
Dr Louis Steven Levene - Corresponding Applicant - University of Leicester
Dr Nicola Walker - Collaborator - University of Leicester
Professor Richard Baker - Collaborator - University of Leicester
Dr Samuel Seidu - Collaborator - Leicester Diabetes Centre

Linkages: 
HES Admitted;ONS;Patient IMD