A flow regulator for a blood collection assembly includes a housing having an inlet and an outlet, which defines an interior space between the inlet and the outlet. A membrane having a first surface and a second surface is disposed at least partially within the interior space. The membrane has a first position where a flow path between the inlet and the outlet is substantially open, and a second position where the flow path between the inlet and the outlet is at least partially restricted. The membrane is configured to move between the first and second positions in response to a pressure differential acting on the membrane.