Abstract: An apparatus, comprising at least separating means (1) for separating blood plasma and red blood cells, which separating means (1) comprise pressure means (20) for pressing at least a part of the blood through a filter (26), wherein at least first collecting means (27) are provided for collecting separated blood plasma and at least one reagent is provided in said first collecting means (27) or can be introduced therein for reaction with substances or organisms present in said blood plasma.