Increased hematocrit with normal red blood cell mass in early borderline essential hypertension

Hematocrit, red blood cell mass, plasma volume and plasma renin activity were evaluated in 33 (15 women) young patients with borderline hypertension and in 30 (15 women) age- and sex-matched normotensive control subjects. Mean hematocrit values were slightly but significantly higher (P less than 0.05) at this early stage of hypertension and it correlated with the elevation of arterial hypertension (r = 0.39, P less than 0.05). Red blood cell mass was normal indicating normal bone marrow production. Plasma volume was significantly contracted (p less than 0.05) and it can account in part for the increased hematocrit and plasma renin activity. These results indicate that the alterations in circulating fluid components and in hematocrit described in moderate to severe forms of hypertension are also present in early borderline hypertension.