Literature Review of Occult Hepatitis B Infection and Hepatitis B Core Antibody-Positive Blood Donors.

Hepatitis B virus (HBV) is one of transfusion-transmissible infection that is screened routinely in blood centers by serology and/or nucleic acid testing (NAT). Serology tests for HBV include antibody to hepatitis B core antigen (anti-HBc) and hepatitis B surface antigen (HBsAg). Blood centers around the world differ in their procedures for screening for HBV in blood donors. In high-income, HBV non-endemic countries, anti-HBc, HBsAg, and pooled NAT are usually used to screen blood donors, while in HBV endemic countries, anti-HBc is not usually used because it would lead to high discard rates. Donors who test positive only for anti-HBc have a history of HBV infection but have cleared the virus, resulting in negative results for both HBsAg and NAT. Deferral policy for anti-HBc-positive-only donors is restricted only to donors with high titers of anti-HBc and low titers of the protective antibody to hepatitis B surface antigen (anti-HBs) in some countries. In HBV endemic countries that screen for HBV by HBsAg and NAT, some blood donors test positive for HBsAg but negative for NAT (NAT yield donors). These test results can be the result of window period infection or occult hepatitis B infection (OBI), defined as the presence of replication-competent HBV DNA in the liver - in the presence or absence of HBV DNA in the blood - of individuals testing negative for HBsAg assessed by currently available assays. OBI donors can transmit HBV to recipients by blood transfusion. Therefore, in HBV endemic countries, individual donation NAT (ID-NAT) should be used to screen blood donors because it is more sensitive than pooled NAT and can detect both window period infection and OBI, while anti-HBc cannot detect window period infection.