The trouble with unreadables: IFA as a useful confirmatory test to resolve HIV EIA RR/WB Unreadable donor samples

S Vanderpool, K-A T Nguyen, A Bond, P Lewithan, and H Kamel. Blood Systems Inc., Scottsdale, AZ, and Blood Centers of the Pacific, San Francisco, CA.

Background: The licensed HIV-1 Western Blot (WB) generally available for confirmatory donor testing has yielded increasing numbers of Unreadable (UNR) results. WB UNR results hinder interpretation and generate high levels of anxiety and confusion among both blood donors and blood center consignees. This study evaluated the utility of repeat HIV-1 WB and HIV-1 immunofluorescence assay (IFA) on donor follow-up samples for resolving the clinical significance of HIV EIA repeat reactive (RR)/WB UNR cases.

Methods: Index donation samples were screened with Genetic Systems HIV-1/2 EIA and Chiron Procleix HIV-1/HCV NAT.  EIA RR samples received confirmatory testing with Genetic Systems HIV-1 WB. For index donations with HIV-1/2 EIA RR/HIV-1 WB unreadable results, donors were contacted to request follow-up testing. Follow-up samples were tested by repeat Genetic Systems HIV-1 WB. Those follow-up samples with repeat WB UNR results were submitted for HIV-1 IFA at the California Viral Testing Laboratory. Donors were deferred permanently and consignee notification was performed based on index donation HIV EIA RR results. Confirmatory and follow-up results were incorporated into subsequent counseling.

Results: For HIV-1/2 EIA RR donor samples from 2004 and 2005, confirmatory HIV-1 WB testing gave inconclusive information in 52% of cases (Table 1). Secondly, the rate of WB UNR results has significantly increased, almost doubling in first quarter, 2005. All index donation UNR cases from 2004-2005 were negative for HIV-1 NAT. Donor follow-up samples from 45% of UNR index cases were available for repeat HIV-1 WB (Table 2). The majority of follow-up samples yielded UNR results on repeat WB. 89% of these repeat WB UNR samples were negative by HIV-1 IFA, and 11% were IFA inconclusive.

Conclusions: The currently available licensed HIV-1 WB has yielded unacceptably high rates of inconclusive and increasingly frequent UNR results. These donors are permanently deferred. WB on follow-up samples was not useful due to the likelihood of repeat UNR results. In contrast, IFA resolved as Negative most WB UNR cases. Due to the low donor return rate, HIV-1 IFA on the index donation would improve donor and consignee counseling and should be considered as an alternative HIV antibody confirmatory method.

Table 1

Table 2