Fluid flow control devices for medical use are disclosed. On one end, a fluid flow control device is configured to be attached to a manifold that is in-line with an infusion setup and the other end of the fluid flow control device is configured to be attached to a sampling or infusion device, such as a syringe. In one aspect, a fluid flow control device has an external casing and an internal casing which is configured to be movably housed within the external casing. The internal casing mates with a fluid outlet on the external casing and upon separating the internal and external casings a fluid flow path is established.