Abstract: A sterile barrel and piston assembly with attached aspirating needle is delivered ready for use. Following removal of a needle shield and a reversible safety cap from the rear of the piston, the needle is inserted in a vein and evacuated blood sample tube is inserted in the piston to be penetrated by the rear end of the needle. Following removal of the needle from the vein and removal of the evacuated tube now containing a blood sample, the piston is turned in one direction relative to the barrel of the device to release a first lock between the barrel and piston, followed by retraction of the piston and turning of the piston in the same direction to activate a second lock between the barrel and piston. The safety cap is reversed and re-applied to the rear of the piston where it becomes permanently locked in place. The needle is now safely enclosed within the barrel rearwardly of a safety shield and membrane on the front of the barrel.