Hepatitis B virus DNA viral load determination in hepatitis B surface antigen-negative Swiss blood donors

Nucleic acid test (NAT) hepatitis B virus (HBV) screening for all blood donations with a sensitivity limit of 25 IU/mL in the individual donation is mandatory in Switzerland since 2009. The aims of the two studies were to define the percentage of antibody to hepatitis B core antigen (anti-HBc) or anti-HBc and antibody to hepatitis B surface antigen (anti-HBs)-positive donors bearing HBV DNA and to gather HBV viral load data on HBV NAT yields during the routine screening since the introduction of the HBV NAT.Archive samples from anti-HBc-positive donors (Group I) were analyzed with a quantitative HBV DNA test and further with anti-HBc and anti-HBs assays. In addition, all the HBV NAT-only-yield samples (Group II) from the routine donor screening performed between July 2007 and May 2013 were included in the study.From the 667 samples investigated (131 donors), three donors (2.3%) had donated eight samples (1.2%) with detectable HBV DNA; however, all had very low viral loads (≤ 10 IU/mL). From the 1,160,426 donations screened with the routine HBV NAT assay, 16 HBV NAT yields were detected: two window period (WP) and 14 occult hepatitis B infection (OBI) cases. In eight of these positive donations (two WP and six OBI), the HBV viral loads were not more than 10 IU/mL, in three cases between 10 and 25 IU/mL, and in the remaining five donations between 37 and 166 IU/mL.The highly sensitive HBV NAT assay with a threshold significantly below 10 IU/mL is a valuable alternative to anti-HBc and a less sensitive HBV NAT screening in blood donor screening.