A device for testing the presence or absence of a substance in blood, comprising: a coupler or hub that is capable of coupling with a needle, wherein the needle is for withdrawing blood from a subject and for introducing the withdrawn blood into the device; a first chamber for receiving the withdrawn blood; a second chamber for receiving at least some of the withdrawn blood from the first chamber; a test strip held within the second chamber; a wall or panel that separates the first chamber from the second chamber; and at least one aperture in the wall or panel configuring for allowing blood to pass from the first chamber to the second chamber, wherein the test strip is capable of producing a visible signal that indicates the presence or absence of the substance in the withdrawn blood, and wherein the second chamber comprises a window for viewing the test strip, the window allowing visual detection of the visible signal, characterised in that: the second chamber comprises a flexible dome, wherein the flexible dome is capable of flexing radially outward to create a partial vacuum that draws blood out of the first chamber and into the second chamber and of flexing radially downwards to increase the pressure within the second chamber; and a sliding latch is operatively linked to the flexible dome and is capable of: being slid over the flexible dome to compress the flexible dome radially downwards and increase the pressure within the second chamber, and being slid away from the flexible dome to release the flexible dome and allow the flexible dome to flex radially outwards to create the partial vacuum in the second chamber. a coupler or hub that is capable of coupling with a needle, wherein the needle is for withdrawing blood from a subject and for introducing the withdrawn blood into the device; a first chamber for receiving the withdrawn blood; a second chamber for receiving at least some of the withdrawn blood from the first chamber; a test strip held within the second chamber; a wall or panel that separates the first chamber from the second chamber; and at least one aperture in the wall or panel configuring for allowing blood to pass from the first chamber to the second chamber, wherein the test strip is capable of producing a visible signal that indicates the presence or absence of the substance in the withdrawn blood, and wherein the second chamber comprises a window for viewing the test strip, the window allowing visual detection of the visible signal, characterised in that: the second chamber comprises a flexible dome, wherein the flexible dome is capable of flexing radially outward to create a partial vacuum that draws blood out of the first chamber and into the second chamber and of flexing radially downwards to increase the pressure within the second chamber; and a sliding latch is operatively linked to the flexible dome and is capable of: being slid over the flexible dome to compress the flexible dome radially downwards and increase the pressure within the second chamber, and being slid away from the flexible dome to release the flexible dome and allow the flexible dome to flex radially outwards to create the partial vacuum in the second chamber. the second chamber comprises a flexible dome, wherein the flexible dome is capable of flexing radially outward to create a partial vacuum that draws blood out of the first chamber and into the second chamber and of flexing radially downwards to increase the pressure within the second chamber; and a sliding latch is operatively linked to the flexible dome and is capable of: being slid over the flexible dome to compress the flexible dome radially downwards and increase the pressure within the second chamber, and being slid away from the flexible dome to release the flexible dome and allow the flexible dome to flex radially outwards to create the partial vacuum in the second chamber. being slid over the flexible dome to compress the flexible dome radially downwards and increase the pressure within the second chamber, and being slid away from the flexible dome to release the flexible dome and allow the flexible dome to flex radially outwards to create the partial vacuum in the second chamber.