To evaluate factors associated with misclassification by the limiting-antigen avidity (LAg-avidity) assay among individuals with long-standing HIV infection.Design:
Samples were obtained from the Multicenter AIDS Cohort Study and AIDS Linked to the IntraVenous Experience cohort (1089 samples from 667 individuals, 595 samples collected 2–4 years and 494 samples collected 4–8 years after HIV seroconversion). Paired samples from both time points were available for 422 (63.3%) of the 667 individuals.Methods:
Samples were considered to be misclassified if the LAg-avidity assay result was 1.5 or less normalized optical density (OD-n) units.Results:
Overall, 4.8% (52/1089) of the samples were misclassified, including 1.8% [16/884, 95% confidence interval (CI) 1.09–3.06%] of samples from individuals with viral loads above 400 copies/ml and 1.4% (10/705) of samples from individuals with viral loads above 400 copies/ml and CD4+ cell counts above 200 cells/μl (95% CI 0.68–2.60%). Age, race, sex, and mode of HIV acquisition were not associated with misclassification. In an adjusted analysis, viral load below 400 copies/ml [adjusted odds ratio (aOR) 3.72, 95% CI 1.61–8.57], CD4+ cell count below 50 cells/μl (aOR 5.41, 95% CI 1.86–15.74), and low LAg-avidity result (≤1.5 OD-n) from the earlier time point (aOR 5.60, 95% CI 1.55–20.25) were significantly associated with misclassification.Conclusions:
The manufacturer of the LAg-avidity assay recommends excluding individuals from incidence surveys who are receiving antiretroviral therapy, are elite suppressors, or have AIDS (CD4+ cell count <200 cells/μl). The results of this study indicate that those exclusions do not remove all sources of assay misclassification among individuals with long-standing HIV infection.