Chen Jincai, a resident of Wenzhou, East China's Zhejiang province, has the Rh negative-type blood, also known as "panda blood" in China as only three in every 1,000 people are carriers of this type of blood.

The 49-year-old said she first donated blood in 2002 after seeing a blood collection vehicle on the street. She was then unaware of the rarity of her blood type, as reported by the Wenzhou Daily, a local newspaper.

In 2003, Chen received a phone call from the city's blood bank asking her to donate to help save the life of a patient with the Rh negative blood, who was in critical condition. She rushed to help the patient immediately.  

Ever since, Chen has donated blood at least once a year, and said she always stopped whatever she was doing when she received phone calls asking for blood.

In the past 15 years, Chen has donated a total of 5,400 millimeters of blood, more than the entire volume in the human body. To better help people in need, she joined a WeChat group for people who have the "panda blood" so she could see messages calling for help in time.

Chen said she exercises regularly to keep in a good shape in order to get ready to donate blood at any time.