Ischaemic heart disease: association with haematocrit in the British Regional Heart Study.

OBJECTIVES To assess the relationship between haematocrit and risk of major ischaemic heart disease events. DESIGN Prospective study of a cohort of men followed up for 9.5 years. SETTING General practices in 24 towns in England, Wales, and Scotland (British Regional Heart Study). SUBJECTS Altogether 7735 men aged 40-59 years at screening, who were selected at random from one general practice in each of 24 towns, were studied. MAIN OUTCOME MEASURES Fatal and nonfatal ischaemic heart disease events. RESULTS Risk of major ischaemic heart disease events was significantly increased at haematocrit levels of > or = 46.0%. Men with raised haematocrit (> or = 46.0%) showed a 30% increase in relative risk (RR) of major ischaemic heart disease events (RR = 1.32; 95% confidence intervals (CI) 1.10,1.57, p < 0.01) compared with those with values below 46.0%, even after adjustment for age, social class, smoking, body mass index, physical activity, blood cholesterol, lung function (FEV1), and pre-existing evidence of ischaemic heart disease. Further adjustment for systolic blood pressure reduced the risk slightly (RR = 1.27; 95% CI 1.06,1.51, p = 0.02) but it remained significant. The relationship was seen in men with and without pre-existing evidence of ischaemic heart disease. The study suggests that an increased haematocrit level plays a part in the development of major ischaemic heart disease events.