BLOOD DONORS AND BLOOD COLLECTION Combination HCV core antigen and antibody assay on a fully automated chemiluminescence analyzer Dinesh O. Shah, Chi D. Chang, Lily X. Jiang, Kevin Y. Cheng, A. Scott Muerhoff, Robin A. Gutierrez, Thomas P. Leary, Suresh M. Desai, Irenea V. Batac-Herman,Vince A. Salbilla, Alla S. Haller, James L. Stewart, and George J. Dawson Volume 43, August 2003 TRANSFUSION 1067 ABBREVIATION: S/CO = signal-to-cutoff ratio. From the New Assay Development and Infectious Diseases R & D, Abbott Diagnostics Division, Abbott Laboratories, Abbott Park, Illinois. Address reprint requests to: Dinesh O. Shah, PhD, Infectious Diseases R & D, Department of 9GN, AP20, Abbott Laboratories, Abbott Park, IL 60064; e-mail: dinesh.shah@abbott.com. Received for publication January 10, 2003; revision received March 14, 2003, and accepted March 18, 2003. TRANSFUSION 2003;43:1067-1074. BACKGROUND: HCV exposure among blood donors is serologically determined by detection of antibodies to HCV (anti-HCV); however, the recent development of an assay for the detection of HCV core antigen identi- fies infection before anti-HCV development. Simultane- ous detection of HCV core antigen and anti-HCV would shorten the window period before seroconversion over conventional HCV antibody screening assays. STUDY DESIGN AND METHODS: A prototype chemi- luminescent immunoassay was developed for simulta- neous detection of HCV core antigen and anti-HCV in human sera and plasma. The assay was performed on a single-channel instrument representing an automated serologic analyzer (PRISM, Abbott Laboratories) system. Sensitivity and specificity were evaluated by testing 23 HCV seroconversion panels and plasma or sera from volunteer blood donors. RESULTS: The prototype HCV core antigen and anti- body combination assay detected 80 of 89 (89.9% ) HCV RNA-positive and antibody-negative specimens from 23 panels, thereby reducing the seroconversion window period by an average of 34.3 days compared to PRISM HCV antibody detection. All PRISM HCV anti- body-positive specimens were detected by the combi- nation assay for a relative sensitivity of 100 percent. The repeatedly reactive rate was 0.20 percent based on testing of 3017 screened anti-HCV-negative sera and plasma. CONCLUSIONS: The prototype combination assay was shown to detect HCV core antigen and anti-HCV simul- taneously and significantly closed the time gap between the initial detection of HCV RNA and the first appear- ance of detectable antibodies to HCV. T ests for antibodies against the HCV have been used for the detection of HCV infection since 1989. 1 The incidence of posttransfusion HCV has declined steadily since the implementation of routine screening of whole blood and plasma for HCV antibodies. 2,3 The HCV second- and third-generation HCV antibody tests have improved detection of individuals infected with all known viral genotypes and have shown earlier detection of seroconversion than the first-genera- tion assays. However, the average window period between HCV infection and seroconversion with new generation of HCV antibody tests remains approximately 70 days. 2 To prevent transmission of HCV during the window period before seroconversion, NAT for HCV has been developed. Its implementation in many developed countries has dra- matically reduced the residual risk for posttransfusional HCV infection. Recent studies indicate that HCV core antigen can be detected in the window period before seroconversion, and HCV core antigen levels correlate well with HCV RNA levels. 4-13 We recently reported on the development of a new HCV core antigen detection assay developed for an automated chemiluminescent analyzer. 9 The antigen assay showed excellent specificity (>99%) and sensitivity relative to NAT of 98.6 percent based on testing of 15 HCV seroconversion panels. Development and implementa- tion of an assay combining the detection of HCV core