A blood collection assembly includes a needle cannula with an intravenous end and a non-patient end. The cannula is mounted to a needle holder so that the non-patient end projects into the holder. A safety shield is telescoped over the needle cannula and is movable from a proximal position where the intravenous end of the cannula is exposed to a distal position where the intravenous end of the cannula is shielded. The safety shield is configured to be passively actuated and propelled into the distal position in response to insertion of a blood collection tube into the holder. However, a slide back actuator extends from the safety shield to permit the shield to be retracted into a proximal position during use and before the safety shield is locked in the distal position.