Assay device and method

An assay device comprising a lid and a base, the base comprising a sample addition zone, a reaction zone and an absorbing zone, each of the zones being in fluid connection and component parts of a defined fluid passage leading from the sample addition zone to the absorbing zone, the assay device further comprising:

• a) a sample addition well integrated in the lid;
• b) the absorbing zone comprising an area on an non-porous substrate defining the base, the absorbing zone having projections that are perpendicular relative to the substrate, the entirety of the absorbing zone being directly covered by a foil in which the foil, the projections and the substrate define a volume which together with the volume of the fluid passage further define a sample volume subjected to the assay device and in which the foil or an adhesive attaching the foil to the projections of the absorbing zone has hydrophilic properties that increase the flow velocity of fluid along the fluid passage;
• c) each of the zones of the defined fluid passage comprising projections perpendicular relative to the base, the projections commonly having a height, diameter and center to center distance between the projections such that lateral capillary flow of the fluid from the sample addition zone toward the absorbing zone along the defined fluid passage is achieved by the projections;
• and
• d) at least one filter disposed between the sample addition well and the sample addition zone, wherein the at least one filter is a hydrophilic polymeric membrane capable of separating red blood cells from plasma, and wherein the at least one filter is in contact with the perpendicular projections in the sample addition zone and in which the flow rate of fluid through the assay device along the defined fluid passage is controlled by selection of the hydrophilic properties of the foil or the adhesive attaching the foil to the projections of the absorbing zone.