title: Avidity Index for anti-HIV antibodies: comparison between third- and fourth-generation automated immunoassays.
abstract: The development of assays for detecting recent HIV infections has become crucial for analyzing trends in infection in different populations, both for surveillance and prevention activities. The anti-HIV avidity index (AI), measured with third-generation immunoassays (which detect anti-HIV antibody), has been shown to be an accurate tool for discriminating recent HIV infections (<6 months) from established infections (≥ 6 months). We compared a third-generation immunoassay (AxSYM HIV 1/2 gO; Abbott Diagnostics) to a fourth-generation immunoassay (Architect HIV Ag/Ab Combo; Abbott Diagnostics; which detects anti-HIV antibody and p24 antigen) in terms of AI performance in distinguishing between recent and established HIV infections. A total of 142 samples from 75 HIV-infected individuals with an estimated date of seroconversion were assayed. The two assays showed the same accuracy in identifying a recent infection (91.5%), using an AI cutoff of 0.80, although Architect HIV Ag/Ab Combo was slightly more sensitive (89.4% versus 84.8%; P > 0.05) and yet less specific (93.4% versus 97.4%; P > 0.05). The correlation between assays was high (r = 0.87). When 20 specimens falling in the gray zone around the cutoff point (0.75 ≤ AI ≤ 0.84) were excluded, the accuracy of AI with Architect HIV Ag/Ab Combo was 94.7%, and the concordance between the two assays was 99.2%. The anti-HIV AI is a serological marker that accurately discriminates recent from established HIV infections. It can be successfully applied on fully automated fourth-generation HIV Ab/Ag immunoassays, which have several advantages, including increased throughput, high reproducibility, no need for specific technical skills, and easy comparability of results obtained in different settings.
authors.affiliation: Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy. suligoi@iss.it
authors.forename: Barbara
authors.initials: B
authors.lastname: Suligoi
authors.forename: Anna
authors.initials: A
authors.lastname: Rodella
authors.forename: Mariangela
authors.initials: M
authors.lastname: Raimondo
authors.forename: Vincenza
authors.initials: V
authors.lastname: Regine
authors.forename: Luigina
authors.initials: L
authors.lastname: Terlenghi
authors.forename: Nino
authors.initials: N
authors.lastname: Manca
authors.forename: Salvatore
authors.initials: S
authors.lastname: Casari
authors.forename: Laura
authors.initials: L
authors.lastname: Camoni
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Salfa
authors.forename: Claudio
authors.initials: C
authors.lastname: Galli
mesh_terms: D000328:Adult; D000915:Antibody Affinity; D001331:Automation / Q000379:methods*; D019411:Clinical Laboratory Techniques / Q000379:methods*; D005260:Female; D006678:HIV / Q000276:immunology*; D015483:HIV Antibodies / Q000276:immunology*; D015658:HIV Infections / Q000175:diagnosis* / Q000276:immunology*; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity
chemical_list: D015483:HIV Antibodies