High remaining risk in poorly treated hypertension: the 'rule of halves' still exists.

OBJECTIVES: To estimate risk factors for stroke, to examine how different categories of patients with increased blood pressure are associated with risk for first-ever stroke event, and to estimate the proportions of these categories in a geographically defined population in northern Sweden.

SETTING: The study was nested within the Västerbotten Intervention Program and the Northern Sweden MONICA cohorts.

DESIGN AND PARTICIPANTS: A population-based cross-sectional study and an incident case-control study were carried out. The incident case-control study comprised 129 cases of first-ever stroke diagnosed during 1985-96, with two randomly selected controls per case, chosen from the same geographically defined population. The cross-sectional study was based on 59,735 participants. Blood pressure status was categorized as: normotensive [systolic blood pressure (SBP) <140 mmHg and diastolic blood pressure (DBP) <90 mmHg]; treated and adequately controlled hypertension (SBP <140 mmHg and DBP <90 mmHg); treated but poorly controlled hypertension (SBP > or = 140 mmHg or DBP > or = 90 mmHg, or both); untreated hypertension (SBP > or = 140 mmHg or DBP > or = 90 mmHg, or both); newly detected increased blood pressure (SBP > or = 140 mmHg or DBP > or = 90 mmHg, or both).

MAIN OUTCOME MEASURE: Risk for first-ever stroke.

RESULTS: In the cross-sectional study, 68% of individuals were normotensive, 3% had treated and adequately controlled hypertension, 6% had treated but poorly controlled hypertension, 7% had untreated hypertension, and 16% had newly detected increased blood pressure. In univariate analysis of the case-control study, history of diabetes, daily smoking, obesity, increased blood pressure and the hypertension categories 'treated but poorly controlled' and 'untreated' were associated with an increased stroke risk. In multivariate logistic regression analysis, only diabetes and the hypertension categories treated but poorly controlled and untreated remained significant, with odds ratios 6.1 (95% confidence interval 2.4 to 15.3) and 4.3 (95% confidence interval 1.7 to 10.5), respectively. Only one of the 129 individuals who suffered stroke had treated and adequately controlled hypertension.

CONCLUSIONS: The study illustrates the importance of adequate blood pressure control and, at the same time, that the vast majority in the population with increased blood pressure did not receive optimal care. Thus the 'rule of halves' still exists, and the high remaining risk in poorly treated hypertensive individuals in Sweden is remarkable and requires attention from the medical profession.