Early assessment of HIV incidence is an important public health tool for understanding the state of the epidemic in a particular area, identifying high-risk groups, and assessing the effectiveness of HIV prevention interventions.Objective. To assess the possibility of using the positivity rate (S/CO) in the HIV Ag/Ab immunoassay on the Alinity i analytical platform to determine the duration of infection during HIV screening.Materials and methods. The study included 316 HIV-infected patients with different infection durations. Immunochemical analysis was performed on an Alinity i automatic analyzer (Abbott Laboratories, USA) using the Alinity i HIV Ag/Ab Reagent Kit (Abbott Laboratories, Germany) in accordance with the manufacturer’s instructions.Results. Statistical analysis of 316 blood samples from HIV-infected patients at different stages of infection demonstrated the reactivity of the Alinity i HIV Ag/Ab test result and a dynamic increase in the positivity ratio during the first six months after the onset of the disease. Based on the data obtained, a threshold value (≤294 conventional units) was obtained for the positivity ratio, which allowed for a clear distinction between HIV-positive patients with a recent (<6 months) period of infection. At the same time, the sensitivity and specificity indicators for detecting recent infection in the CMIA analysis were 79,0% and 63,2%, respectively.Conclusion. The additional usage of the positivity ratio in the Alinity i HIV Ag/Ab CMIA analysis meets the acceptability criteria for assessing the duration of HIV infection and can be a useful tool for analyzing the stage of the epidemic in a particular territory.