Improved efficiency of national HIV, HCV, and HTLV antibody testing algorithms based on sequential screening immunoassays.

BACKGROUND: Traditional strategies for clarifying the antibody status of donors giving repeatedly reactive (RR) results on primary screening immunoassays (IA1) have usually involved direct testing by immunoblot. However, such strategies can generate nonspecific in determinate results. The aim of this report is to present the results of an alternative strategy based on the use of sequential immunoassays (SI) before immunoblot testing. STUDY DESIGN AND METHODS: The efficiency of traditional and SI strategies was compared in terms of the number of IA1 RR samples requiring immunoblot testing and the percentage of immunoblot tests giving indeterminate results. In addition, the biologic false- reactive overlap between the PRISM assays selected as IA1 and candidate secondary screening immuno- assays (IA2) was calculated to determine the most efficient IA1/IA2 combinations. RESULTS: There was a significant decrease in the proportion of IA1 RR samples requiring immunoblot testing under the SI strategy when compared with existing site-specific strategies for HIV (0.49 vs. 0.08, p < 0.05), HCV (0.85 vs. 0.42, p < 0.05), and HTLV (0.69 vs. 0.05, p < 0.05) algorithms. In addition, there was a significant decrease in the percentage of immunoblot tests giving indeterminate results for HIV and HTLV under the SI strategy. However, there was no significant difference in the proportion of confirmed positive results for HIV, HCV, or HTLV before and after national SI algorithm implementation. For the anti-HIV IA2s, there was considerable variation of biologic false-reactive overlap with the PRISM HIV O plus chemiluminescent immunoassay (range, 1.6-15.6%). CONCLUSIONS: The results presented in this report demonstrate that the sequential use of screening immunoassays before immunoblot testing can significantly reduce both the number of immunoblot tests and proportion of indeterminate results, without impacting sensitivity, thereby improving algorithm efficiency and simplifying donor management.

Assessing the accuracy of three viral risk models in predicting the outcome of implementing HIV and HCV NAT donor screening in Australia and the implications for future HBV NAT.

BACKGROUND: Risk modeling is now the most practical method of estimating the residual risk of viral transmission in developed countries. One method of assessing the accuracy of a risk model is to measure the observed against the predicted outcome after implementing a new screening method. The primary objective of this paper is to assess the accuracy of three published models in predicting the impact of implementing HIV and HCV NAT in Australia. STUDY DESIGN AND METHODS: Viral screening data on Australian donors for 2000 and 2001 were retrospectively analyzed. The data were applied to the three models to estimate the risk of transmission and predicted NAT yield for HIV, HCV, and HBV. RESULTS: The median risk estimates for the three models were 1 in 3,415,000 for HIV NAT, 1 in 911,000 for HCV NAT, and 1 in 483,000 for HBsAg. The predicted NAT yield for the three models ranged from 0.17 to 0.30 per million donations for HIV, 1.20 to 5.55 for HCV, and 0.47 to 1.01 for HBV. The observed NAT yield was not significantly different from the expected yield with any of the three models for either HIV or HCV. CONCLUSIONS: First, the residual risk in Australian donors is small in comparison with other transfusion complications and comparable to or lower than the risk in US and European nonremunerated donors. Second, mathematical risk modeling has sufficient precision to be used as a predictive tool for risk-benefit assessments of novel screening procedures. Finally, in relation to the case for implementing HBV NAT and/or anti-HBc in Australia, we conclude that at present, there is inadequate information about our donor population to perform an evidence-based risk-benefit analysis.