Microfluidic test carrier for apportioning a quantity of fluid into subquantities, having a substrate and a covering layer and having a capillary structure formed in the substrate that is enclosed by the substrate and the covering layer, wherein - the capillary structure comprises a receiving chamber, a sample chamber (8, 10, 11) and a connecting channel between the receiving chamber and the sample chamber (8, 10, 11), - the receiving chamber has two opposite boundary surfaces (22, 23) and a side wall, wherein one of the boundary surfaces (22, 23) has an inlet port and one of the boundary surfaces is the floor of the receiving chamber and the other boundary surface is the cover of the receiving chamber, characterized in that - the receiving chamber has a circumferential venting channel and a circumferential dam positioned between the receiving chamber and the venting channel, wherein the dam is formed by a wall and forms a side wall of the venting channel and is closer to the inlet port than the venting channel, - the dam is designed such that the height of the wall is less than the height of the radially outer side wall of the venting channel so that a gap occurs between the covering layer of the test carrier and the upper side of the wall, the height of the gap being less than the height of the venting channel so that a capillary stop forming a geometric valve is formed with the venting channel through which air can escape out of the venting channel, - the connecting channel extends between an outflow orifice of the venting channel and an inlet orifice of the sample chamber (8, 10, 11) such that fluid transport is possible from the receiving chamber into the sample chamber (8, 10, 11), and - the valve is designed such that automatic fluid transport out of the receiving chamber is prevented. - the capillary structure comprises a receiving chamber, a sample chamber (8, 10, 11) and a connecting channel between the receiving chamber and the sample chamber (8, 10, 11), - the receiving chamber has two opposite boundary surfaces (22, 23) and a side wall, wherein one of the boundary surfaces (22, 23) has an inlet port and one of the boundary surfaces is the floor of the receiving chamber and the other boundary surface is the cover of the receiving chamber, - the receiving chamber has a circumferential venting channel and a circumferential dam positioned between the receiving chamber and the venting channel, wherein the dam is formed by a wall and forms a side wall of the venting channel and is closer to the inlet port than the venting channel, - the dam is designed such that the height of the wall is less than the height of the radially outer side wall of the venting channel so that a gap occurs between the covering layer of the test carrier and the upper side of the wall, the height of the gap being less than the height of the venting channel so that a capillary stop forming a geometric valve is formed with the venting channel through which air can escape out of the venting channel, - the connecting channel extends between an outflow orifice of the venting channel and an inlet orifice of the sample chamber (8, 10, 11) such that fluid transport is possible from the receiving chamber into the sample chamber (8, 10, 11), and - the valve is designed such that automatic fluid transport out of the receiving chamber is prevented.