plasma to maximize the plasma which reaches the membrane 40 this is desirable as it results in requiring less blood from the user if present the spreading screen 20 is less dense than the separating layer 30 thus mesh size openings found in the separating layer 30 are smaller than that for the spreading screen 20 preferably from 20 to 200 microns the amount of fabric occupied by voids is preferably 15 to 60 a preferred fabric for the separating layer is polyester cotton or a 50 50 polyester cotton blend the separating layer 30 is preferably pretreated with a blood cell separating agent prior to assembly to enhance filtration the blood cell separating agents imbibed in the separating layer 30 may be any agent known by a practiced artisan to bind to red blood cells without lysing them these agents include lectins antibodies to red blood cells water soluble salts with potassium citrate ammonium sulfate zinc sulfate and the like lectins are preferred and include proteins or glycoproteins that recognize specific sequences of polysaccharide residues the lectin or other binding agent is applied by dipping the separating layer fabric into a solution of the lectin or other agent and allowing the wetted fabric to air dry the solution can be prepared in concentrations that are easily handled in standard test strip manufacturing equipment typically 2 7 solutions are acceptable the separating layer 30.