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J Intern Med. 1994 Feb;235(2):163-8.

Haematocrit, hypertension and risk of stroke.

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1
Department of Public Health and Primary Care, Royal Free Hospital School of Medicine, London, UK.

Abstract

OBJECTIVES:

To assess the relationship between haematocrit and risk of stroke.

DESIGN:

Prospective study of a cohort of men followed up for 9.5 years.

SETTING:

General practices in 24 towns in England, Scotland and Wales (British Regional Heart Study).

SUBJECTS:

A total of 7735 men aged 40-59 years at screening, selected at random from one general practice in each of 24 towns.

MAIN OUTCOME MEASURES:

Fatal and non-fatal strokes.

RESULTS:

During a follow-up period of 9.5 years for all men there were 123 stroke events (33 fatal) in the 7346 men in whom the haematocrit level had been determined. In the cohort as a whole, risk of stroke was significantly raised at haematocrit levels > or = 51% (relative risk [RR] = 2.5; 95% confidence intervals [CI] 1.2-5.0) after adjustment for age, social class, smoking, body mass index, physical activity, presence of diabetes and pre-existing ischaemic heart disease. Further adjustment for systolic blood pressure did not attenuate this association (RR = 2.4; 95% CI 1.2-4.9). A raised haematocrit was associated with an increase of stroke only in men with hypertension (systolic blood pressure > or = 160 mmHg or diastolic blood pressure > or = 90 mmHg or on regular antihypertensive treatment). No increased risk of stroke was seen at the higher haematocrit level (> or = 51%) in normotensive men. At haematocrit levels below 51%, hypertension was associated with a three-fold increase in risk of stroke compared with normotension (RR = 3.4, 95% CI 2.3, 5.1). At haematocrit levels > or = 51%, hypertension was associated with a nine-fold increase in risk of stroke compared with normotension (RR = 9.3; 95% CI 4.2, 21.0). Exclusion of men receiving regular antihypertensive therapy did not alter the strong associations seen.

CONCLUSION:

The data suggest that an elevated haematocrit is an independent risk factor for stroke and that it interacts synergistically with elevated blood pressure.

PMID:
8308479
[Indexed for MEDLINE]
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