Hematocrit levels and physiologic factors in relationship to cardiovascular risk in Tecumseh, Michigan.

Objective: To investigate the relationship between hematocrit, blood pressure and other known cardiovascular risk factors. Design: The Tecumseh Blood Pressure Study includes a cohort of subjects of average age 29.5 years (346 male, 277 female) who reside in Tecumseh, Michigan, USA. Methods: The body weight; home, work and clinic blood pressures; hematocrit level, plasma renin activity, baseline and mentally stimulated plasma catecholamines level; and fasting glucose, insulin and lipids levels were obtained. Since menstruation and childbearing affect the hematocrit, results are presented only for males. The males in Tecumseh were divided into tertiles of hematocrit (group I less than or equal to 43.25, group II 43.26-45.2 and group III >45.2%). Results: Higher hematocrit levels were significantly related to higher blood pressures at home, at work and in the clinic, although all of the values measured were within the normotensive range (128/79 mmHg clinic blood pressure in group III). The metabolic factors weight, cholesterol, triglycerides, insulin and glucose levels were significantly elevated in group III. The weight affected only the relationship of hematocrit to plasma insulin levels and not the other variables including the blood pressure. Groups II and III showed signs of sympathetic overactivity; their plasma renin levels, heart rates and norepinephrine levels after mental stimulation were elevated. Conclusions: Although the relationship of blood pressure to the hematocrit level was previously known, in Tecumseh hematocrit is also found to be associated with several other cardiovascular risk factors and with signs of a hypersympathetic state. We intend to evaluate prospectively the relative prognostic significance of a higher hematocrit level versus the other associated risk factors.