Defining and validating chronic diseases
Methods Cox proportional hazards models in the derivation cohort to derive separate risk equations in men and women for evaluation at 10 years.
Risk factors considered included those already in QRISK2 (age, ethnicity, deprivation, systolic blood pressure, body mass index, total cholesterol: high density lipoprotein cholesterol ratio, smoking, family history of coronary heart disease in a first degree relative aged less than 60 years, type 1 diabetes, type 2 diabetes, treated hypertension, rheumatoid arthritis, atrial fibrillation, chronic kidney disease (stage 4 or 5)) and new risk factors (chronic kidney disease (stage 3, 4, or 5), a measure of systolic blood pressure variability (standard deviation of repeated measures), migraine, corticosteroids, systemic lupus erythematosus (SLE), atypical antipsychotics, severe mental illness, and HIV/AIDs).
7.89 million patients aged 25-84 years were in the derivation cohort and 2.67 million patients in the validation cohort.
Patients were free of cardiovascular disease and not prescribed statins at baseline.
The ICD-10 codes used were G45 (transient ischaemic attack and related syndromes), I20 (angina pectoris), I21 (acute myocardial infarction), I22 (subsequent myocardial infarction), I23 (complications after myocardial infarction), I24 (other acute ischaemic heart disease), I25 (chronic ischaemic heart disease), I63 (cerebral infarction), and I64 (stroke not specified as haemorrhage or infarction).
Using the QResearch database (version 41) we undertook a cohort study in a large population of primary care patients.
In women, the algorithm explained 59.6% of the variation in time to diagnosis of cardiovascular disease (R, with higher values indicating more variation), and the D statistic was 2.48 and Harrell’s C statistic was 0.88 (both measures of discrimination, with higher values indicating better discrimination).
The corresponding values for men were 54.8%, 2.26, and 0.86.
Main outcome measures Incident cardiovascular disease recorded on any of the following three linked data sources: general practice, mortality, or hospital admission records.
Results 363 565 incident cases of cardiovascular disease were identified in the derivation cohort during follow-up arising from 50.8 million person years of observation.