This study was a collaborative effort between the Institute of Blood Transfusion (IBT) of the Chinese Academy of Medical Sciences and six blood centers located in different regions of China. The six Chinese regional blood centers were the Anhui Blood Center (Hefei, Anhui, located in the east), Fujian Blood Center (Fuzhou, Fujian, located in the south), Dalian Blood Center (Dalian, Liaoning, located in the north), Changzhi Blood Center (Changzhi, Shanxi, located centrally), Kaifeng Blood Center (Kaifeng, Henan, located centrally) and Mianyang Blood Center (Mianyang, Sichuan, located in the west). Figure 1 shows the geographic distribution of the six blood centers. The study population consisted of all blood donors who donated at one of the six participating blood centers or at one of their mobile blood collection vehicles between July 1, 2014 and June 30, 2015. All blood donations were screened with the serological tests for HIV, HBV, HCV and syphilis. All samples of HBsAg reactive screening were sent to the IBT national reference laboratory for blood donor testing, and then were subjected to the HBsAg neutralization test and anti-HBc tests. Residual risks could be calculated by the HBV yield approach as Li et al. described .