Abstract: A lateral flow immunoassay device includes a porous test strip, a sampling channel having an inlet at a first end to receive a biomarker and an outlet at a second end, opposite the first end, the outlet communicating with the test strip. The sampling channel has an air vent opening at or adjacent the second end thereof, and a diluent reservoir having an outlet communicating with the test strip. The outlet of the sampling channel and the outlet of the diluent reservoir are sealed by a common removable seal to prevent communication between the sampling channel and the test strip, and the diluent reservoir and the test strip, until the seal is removed.