The complete blood count is a commonly performed blood test, and previous small studies have suggested that the counts of some types of white blood cell in the complete blood count may be related to the onset of cardiovascular diseases such as stroke and heart attack. This is of interest because this information may help to predict strokes or heart attacks and may guide new therapies which act on white blood cells to reduce the risk of cardiovascular disease.

The hypothesis is that counts of particular types of white blood cell are associated with a range of cardiovascular diseases.

There is evidence from epidemiological studies that counts of some types of white blood cell, such as neutrophils, are associated with increased incidence of coronary disease. Associations with other initial presentations of cardiovascular diseases have not been studied in large cohorts, but may be of interest for use in risk prediction or to guide therapeutic strategies.

The aim of this study is to estimate associations between counts of lymphocytes, neutrophils, eosinophils, monocytes and basophils, and initial presentation of a range of cardiovascular diseases.

The study will use data from the CALIBER dataset of clinically collected electronic health record data from England. Patients enter the study when they have a full blood count (complete blood count) recorded in the dataset, and they are followed up until they experience one of the cardiovascular endpoints, death or transfer out of the participating primary care practice.

This study is part of the CALIBER (Cardiovascular disease research using linked bespoke studies and electronic records) programme funded over 5 years from the National Institute for Health Research (NIHR) and Wellcome Trust. The central theme of the CALIBER research is linkage of the Myocardial Ischaemia National Audit Project (MINAP) with primary care (Clinical Practice Research Datalink) and other resources. The overarching aim of CALIBER is to better understand the aetiology and prognosis of specific coronary phenotypes across a range of causal domains, particularly where electronic records provide a contribution beyond traditional studies. CALIBER has received both Ethics approval (ref 09/H0810/16) and ECC approval (ref ECC 2-06(b)/2009 CALIBER dataset).

Inclusion Criteria:

• All patients aged 30 and over, registered with a participating general practice during the study period.

Exclusion Criteria:

• Patients without a measurement of full blood count during the study period.
• Patients with prior atherosclerotic disease, as recorded in primary care or hospitalisation data.

Cohort study of patients in the CALIBER database who have a record of a full blood count (complete blood count) during the study period while registered at one of 225 general practices contributing data to CPRD (the Clinical Practice Research Datalink) and consenting to data linkage.