The study of anaemia-related haemostasis impairment in haemodialysis patients by in vitro closure time test.

It is known that anaemia in haemodialysis patients could contribute to haemostasis impairment. However, the precise relation between the degree of anaemia and the degree of haemostasis impairment is not known, nor the optimal level of hematocrit above which anaemia no longer disturbs haemostasis. Our study addresses these clinically relevant questions by employing in vitro closure time test, a new method in which the process of platelet adhesion and aggregation following vascular injury is simulated in vitro in samples of whole blood. We studied 63 haemodialysis patients, with 30 age-matched, healthy controls. Results show that patients with hematocrit below 0.32 (N=28) had significantly impaired primary haemostasis, in contrast to patients with hematocrit above 0.32 (N=35), as measured by both types of closure time test. A significant negative association was found between hematocrit values and closure time (CEPI cartridges: rho=-0.41, p<0.001; CADP cartridges: rho=-0.47, p<0.001). A multiple logistic regression model for predicting prolonged closure time confirmed this finding. Nonparametric curve fitting enabled estimation of the level of hematocrit at which the values of in vitro closure time in haemodialysis patients do not differ from those in the controls at approximately 0.35. ROC analysis confirmed this to be the optimal threshold for predicting prolonged closure time for both cartridges. By using in vitro closure time test, we confirmed that anaemia correlates with the severity of haemostasis impairment. We estimated the target level of hematocrit above which anaemia no longer affects haemostasis to be about 0.35. These new results (and new assay) appear to have clinical value for treating haemodialysis patients.