Abstract: A filtration unit to selectively remove leukocytes from fluids containing platelets and systems including a filtration unit are provided. In one embodiment, a filtration unit is provided including an outer casing enclosing a porous element which includes a leukocyte-removal medium with a coating. The coating includes a polymer containing a main hydrophobic chain and a hydrophilic poly(ethylene oxide) side chain and having a mass average molar mass in the range of from about 1,000 g/mol to about 20,000 g/mol. The hydrophilic poly(ethylene oxide) side chain includes from 9 to 50 ethylene oxide units, and the mass percentage of the poly(ethylene oxide) side chain is less than about 50% of the mass average molar mass of the polymer.