Influence of age and hematocrit on the coagulation of blood

摘要

To examine the effects of age, hematocrit and the daily variation in hematocrit on coagulation of blood, the time of onset of coagulation (Ti) of whole blood obtained from donors including normal subjects and patients was measured by means of a rheological technique. The Ti value of recalcified blood decreased with an increase in age, but in donors aged 65 years or more (the elderly), the Ti value was almost independent of age. The Ti value for blood obtained from the elderly was significantly lower at lower hematocrit levels, but that for blood obtained from young donors was almost independent of hematocrit. The daily variation in hematocrit in individuals was small (maximum variation: about 4%), and the variation had little effect on the Ti value. However, a slight increase in hematocrit was considered to bring about a significant increase in viscosity at lower shear rates. Therefore, it is suggested that a slight increase in hematocrit under stagnant flow conditions is one of major risk factors for venous thrombogenesis, especially in the elderly.