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Haematocrit, hypertension and risk of stroke
G Wannamethee1, I J Perry, A G Shaper
1Department of Public Health and Primary Care, Royal Free Hospital School of Medicine, London, UK.
Insights
Elevated haematocrit is an independent risk factor for stroke, particularly in men with hypertension. This study highlights the synergistic interaction between high haematocrit and high blood pressure in increasing stroke risk.
Area of Science:
- Cardiovascular Medicine
- Epidemiology
- Hematology
Background:
- Haematocrit, a measure of red blood cell volume, is a key indicator of blood viscosity.
- Previous studies have suggested a link between elevated haematocrit and cardiovascular events, but its independent role in stroke risk requires further elucidation.
- Understanding factors influencing stroke risk is crucial for developing effective prevention strategies.
Purpose of the Study:
- To investigate the association between haematocrit levels and the risk of stroke in a large cohort of middle-aged men.
- To determine if elevated haematocrit is an independent predictor of stroke, even after accounting for other known risk factors.
- To explore potential interactions between haematocrit and other cardiovascular risk factors, such as hypertension and blood pressure.
Main Methods:
- Prospective cohort study involving 7735 men aged 40-59 years.
- Follow-up period of 9.5 years with data collected from general practices across England, Scotland, and Wales (British Regional Heart Study).
- Assessment of fatal and non-fatal stroke events, with adjustments for various cardiovascular risk factors including age, social class, smoking, BMI, physical activity, diabetes, and pre-existing ischemic heart disease.
Main Results:
- A significantly increased risk of stroke was observed in men with haematocrit levels of 51% or higher (relative risk [RR] = 2.5).
- This association remained significant even after adjusting for multiple cardiovascular risk factors and systolic blood pressure.
- The elevated stroke risk associated with high haematocrit was primarily observed in men with hypertension, indicating a synergistic interaction.
Conclusions:
- Elevated haematocrit is an independent risk factor for stroke.
- A synergistic interaction exists between high haematocrit and elevated blood pressure in increasing stroke risk.
- These findings underscore the importance of monitoring haematocrit levels, especially in hypertensive individuals, for stroke prevention.
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.