Isolated reduction of haematocrit does not compromise in vitro blood coagulation

Low haematocrit values are generally well tolerated in terms of oxygen tran sport but a low haematocrit might interfere with blood coagulation. We thus sampled 60 ml of blood in 30 healthy volunteers. The blood was centrifuged for 30 min at 2000 g and separated into plasma, which contained the platel et fraction, and packed red blood cells. The blood was subsequently reconst ituted by combining the entire plasma fraction with a mixture of packed red blood cells, 0.9% saline, so that the final haematocrit was either 40, 30, 20, or 10%. Blood coagulation was assessed by computerized Thrombelastogra ph(R) analysis. Data were compared using repeated measures analysis of vari ance and post-hoc paired t-tests with Bonferroni correction. Decreasing the haematocrit from 40 to 10% resulted in a shortening of reaction time (r) a nd coagulation time (k), and an increase in angle cc, maximum amplitude (MA ) and clot strength (G) (all P<0.02). This pattern represents acceleration of blood coagulation with low haematocrit values. The isolated reduction in haematocrit, therefore, does not compromise in vitro blood coagulation.