Human T-lymphotropic virus antibody screening of blood donors: rates of false-positive results and evaluation of a potential donor reentry algorithm.

BACKGROUND: Blood donor screening with enzyme immunoassays (EIAs) for antibodies to human T-lymphotropic virus (HTLV)-I, and later to HTLV-I/II, has led to the unnecessary deferral of tens of thousands of individuals. The licensure of the Abbott PRISM HTLV-I/HTLV-II chemiluminescent immunoassay (ChLIA) may permit the reinstatement of historically deferred donors. STUDY DESIGN AND METHODS: The efficacy of a reentry algorithm involving a follow-up sample from EIA-deferred donors testing HTLV-I/II ChLIA nonreactive was evaluated using 386 serologic confirmed-positive samples archived since the inception of anti-HTLV donor screening. Reactivity of the 386 samples by the ChLIA, when coupled with the package insert sensitivity data, may be used to demonstrate efficacy of the reentry algorithm. Donor incidence was also examined from 2008 through 2009 to evaluate changes to the existing HTLV screening policy.
RESULTS: From January 1, 1995, to April 28, 2008, a total of 64,052 donors to the American Red Cross were deferred solely because of HTLV EIA false positivity, representing more than 130,000 US donors. HTLV ChLIA identified 386 confirmed-positive donations from 386 randomly selected donors representing reactivity to both the bioMérieux and the Abbott HTLV-I/II EIAs (95% confidence interval [CI], 99.2%-100%); both EIAs have since been discontinued. This is comparable to the detection of 843 of 843 confirmed-positive samples during the ChLIA clinical trials (95% CI, 99.48%-100%). Incident HTLV infections occurred primarily among female repeat donors during 2008 throughout 2009.
CONCLUSIONS: Donors testing falsely positive by historic EIAs since 1988 should be considered for reinstatement if a contemporary sample tests ChLIA nonreactive. Changes to the existing screening algorithm seem unlikely since new HTLV infections were detected among repeat donors.