The Utility of Multiplex NAT in Blood Screening

摘要

Blood screening is characterized by large throughput of samples containing rare markers of infectious agents that compromise the safety of the recipients. In order to remain cost-effective, screening requires maximum sensitivity to identify low concentration of the targeted markers but also very high specificity in order to limit the deferral of units erroneously identified as infectious. With the considerable progresses made over the last 20 years in both of these critical parameters as well as in the automation of the screening process, the performance of serological assays detecting markers such as HBsAg, anti-HIV, and anti-HCV has reduced the risk of transmission by transfusion of the corresponding agents in a range of 1:50,000 to 1:1.5M. As a result, further risk reduction addressing the window period of infec-tivity preceding the detectability of serological markers or, in the case of HB V, following the disappearance of a detectable serological marker, has been characterized by an extremelylow cost-effectiveness. Despite a situation in which the cost per Quality Adjusted Life Year (QALY) exceeded 1M dollar instead of the generally accepted 50,000 dollar threshold, the government and public willingness to pay for "no risk" blood encouragedtransfusion scientists and diagnostic companies to develop genomic screening for the main infectious viral agents (HBV, HIV, HCV) and others such as human erythrovirus (HErV, formerly parvovirus B19), West Nile virus or Hepatitis A virus. The considerable cost of these new technologies, to a large extent related to patent charges, instigated the development of several options intended to reduce the cost of nucleic acid testing (NAT). Plasma pooling ranging between 8 and 500 samples had the disadvantageof reducing sensitivity, an inconvenience partially reduced in some cases by procedures aiming at concentrating the targeted agents. Multiplexing, a procedure enabling simultaneous screening for two-four nucleic acid targets, was developed. This approachreduces reagent costs, the volume of sample to process, and the time required to obtain results, but at the same time considerably complicates the already multi-step and delicate methods developed for single agent NAT. This review will describe the multiplexes currently available commercially or developed internally by a range of transfusion or regulatory establishments, as well as review the various technical problems attached to this type of methods and provide some examples of their clinical applications.