Understanding and diagnosing occult hepatitis B infection (OBI) still presents an obstacle in managing HBV infection. OBI poses a problem in screening blood donors and managing transfusion procedures. The key identifier of OBI is the presence of HBV-DNA that can only be detected using DNA assays. Nucleic acid testing (NAT) or Real Time Polymerase Chain Reaction (PCR) quantifies HBV-DNA levels in units per ml [IU/ml] or copies, per ml to assess the amount. Even if the donor is HBsAg negative, they can transmit OBI to the recipient by their viremic status (detection of HBV DNA). As a result, it is well worth developing strict screening criteria and reliable tests to identify suspected OBI in blood donors and avoid the chance of HBV transmission through unscreened blood transfusion. In all, we need to consider how prevalent OBI may be among blood donors. Moreover, continuous monitoring is required because the prevalence rates differ across studies conducted in different populations. Furthermore, many infected individuals will eventually manifest liver damage and progress to cirrhosis and hepatocellular carcinoma. Accordingly, OBI is not only important in terms of transmission of infection through blood transfusion, but also has other clinical significance.