People show their certifications of Rh negative blood donation at Tianjin United Family Healthcare in Tianjin Municipality, North China, March 17, 2012. The city's first Rh negative blood donation site was set up here Saturday. More than 70 teachers from an international school donated blood at the site. (Xinhua/Zhou Wei)

People donate Rh negative blood in a blood donation vehicle at Tianjin United Family Healthcare in Tianjin Municipality, North China, March 17, 2012. The city's first Rh negative blood donation site was set up here Saturday. More than 70 teachers from an international school donated blood at the site. (Xinhua/Zhou Wei)