Need for Quality Assurance Program of Donor Screening Tests

Transfusion of blood and blood preparations is indispensible in modern medicine, and the processes of delivering a transfusion to a patient provide additional opportunity for risk, despite the remarkable progress. A spectrum of blood-borne infectious agents is transmitted through transfusion of infected blood donated by apparently healthy and asymptomatic blood donors. The diversity of infectious agents includes hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency viruses (HIV-1/2), human T-cell lymphotropic viruses (HTLV-I/II), Cytomegalovirus (CMV), Parvovirus B19, West Nile Virus (WNV), Dengue virus, trypanosomiasis, malaria, and variant CJD[1]. Post-transfusion hepatitis caused by HBV or HCV make up the major problems of blood-transmitted infections. Clinical characteristics, such as pathophysiology and clinical progress, of post-transfusion hepatitis are the same as those of hepatitis by other causes, except of transmission route. HBV presents a higher residual risk of transmission by transfusion than HCV or HIV. While most infectious blood units are removed by new testing methods such as chemiluminescent serologic assays for hepatitis B surface antigen (HBsAg), there is clear evidence that transmission by HBsAg-negative components occurs, in part, during the serologically negative window period, but more so during the late stages of chronic infection that HBV DNA could be detected despite HBsAg seronegativity defined as occult HBV infection (OBI). OBI is a challenging clinical entity, recognized by two main characteristics: absence of HBsAg, and low viral replication. The frequency of OBI depends on the relative sensitivity of both HBsAg and HBV DNA assays. It also depends on the prevalence of HBV infection in the population. OBI may follow recovery from infection, displaying antibody to hepatitis B surface antigen (anti-HBs) and persistent low-level viraemia, escape mutants undetected by currently available HBsAg assays, or healthy carriage with antibodies to hepatitis B e antigen (anti-HBe) and to hepatitis B core antigen (anti-HBc)[2]. Over time, in the latter situation, anti-HBe and, later, anti-HBc may become undetectable. Blood donated in the stage of so-called 'window period' after exposure is more infectious than that of OBI. It is reported that blood from donors in window period can infect, even if there might be only 10 virus particles because of its high infectivity. On the other hand, in case of chronic HBV infections in which HBsAg is negative or carriers lasting proliferation of HBV, Dane particles have been developing immune complexes with antibodies like anti-HBs, so infectivity is weaker than acute window period. By look-back study[3] reported in Japan, serological responses showing acute infection have been observed in 12 (19%) among 158 patients transfused with HBV-infected blood. Among them, serological responses showing