PURPOSE: To prevent the dissipation of effective components from blood by constituting the above membrane of a hollow polyether sulfone hollow yarn membrane which is of respectively specific values in the permeation rate of bovine serum albumin and permeation rate of pure water and has a specific bore or below.

CONSTITUTION: The hollow yarn membrane used for the blood thickening device consists of the hollow polyether sulfone membrane which has the performance of 20-70% permeation rate of the bovine serum albumin and ≥700l/m2.hr.kg/ cm2 (25°C) permeation rate of the pure water and ≤220μm bore. The polyether sulfone is engineering plastic having heat resistance and is soluble in polar org. solvents; therefore, the ultrafiltration membrane having a desired pore size is formable. The hollow yarn membrane having ≤220m bore is used. Since solid contents are contained at about 20-40% in the blood, the permeation rate cannot be increased unless the flow rate on the membrane surface is increased. However, hemolysis arises if the blood is supplied to the membrane by increasing the pump pressure and, therefore, the shearing rate on the membrane surface is determined by adjusting the membrane diameter.