Sensitivity and interobserver variability of the Recombigen-HIV-1 LA test

Abstract

The Recombigen-HIV-1 LA Test (Cambridge BioScience Corporation, Worcester, MA) uses recombinant peptides derived from the env gene product in a latex agglutination assay for the detection of antibodies to human immunodeficiency virus type 1 (HIV-1) and was recently approved by the Food and Drug Administration for marketing in the United States. It is intended for use as a screening test in physicians' offices, emergency rooms, and other settings where enzyme immunoassays are not practical or available. Concern has been raised over the sensitivity, specificity, and difficulty in interpretation of the agglutination pattern. The authors report on the sensitivity and interobserver variability of the assay as performed in a blinded fashion in a hospital laboratory by technologists experienced with other latex agglutination assays. In the first study, sera from 50 patients positive by enzyme immunoassay (EIA) (Abbott HIV EIA) and western blot (WB), performed with EPITOPE HIV western blot strips were assayed by one technologist using the latex agglutination technique. Forty-six samples were positive and four were negative, yielding a sensitivity of 92%. In the second study, 30 samples consisting of 10 negative by EIA and WB, 10 borderline by EIA and/or indeterminate by WB, and 10 positive by EIA and WB were evaluated by three technologists with the latex agglutination technique. There was agreement among all three technologists in 24 of 30 samples (80%). There was disagreement over one sample from the negative group (one technologist obtained a single false positive result), three from the borderline/indeterminate group, and two from the positive group (three technologists obtained false negative results on two samples). In summary, the authors report interobserver variation in interpreting 20% of tests, reflecting difficulty in assessing weak agglutination. Sensitivity of 92% is below that achievable with the EIA or WB techniques and limits the usefulness of the latex agglutination assay as a screening test.