Hypertension is defined as any of the following:
* Diagnosis of hypertension during a consultation in primary care
* Diagnosis of hypertension (primary or secondary) during a hospitalisation
* Based on continuous blood pressure readings: presence of at least 3 systolic or diastolic high blood pressure readings within a 1 year period (SYS_BP >= 150 mmHg OR DIAS_BP >= 90 mmHg), or at least 2 systolic or diastolic high blood pressure readings within a 6 month period. For diabetic patients and patients over 60 years old, a lower threshold is used (SYS_BP >= 140 mmHg OR DIAS_BP >= 90 mmHg).
* Based on medication: at least two prescriptions of blood pressure lowering medication within 6 months from British National Formulary chapters 2.2.1 (Thiazides), 2.2.3 (loop diuretics), 2.2.4 (Potassium-sparing diuretics with other diuretics), 2.4 (beta blockers), 2.5 (hypertension and heart failure related medication) and 2.6.2 (calcium-channel blockers).