Variables influencing the Thrombostat 4000: recommended standardization.

The in vitro bleeding test (IVBT) (Thrombostat 4000) was performed on blood samples from healthy blood donors using a "preliminary standard test." Only one factor of the test procedure was changed each time. We found the following parameters to have a significant influence on the test results: time interval between sampling and testing, diameter of the filter's aperture, capillary diameter, aggregating agents and their concentration, temperature of the blood and cartridges, method of drying the capillaries, the aspiration pressure, and the hematocrit of the blood sample. According to our data, we propose a standard IVBT for routine application and modifications for special diagnostic use.