PROJECT SUMMARY HIV testing is the entry point into HIV prevention and care and therefore critical for reducing ongoing transmission and morbidity. Although most people with HIV in the U.S. are aware of their infection, many are diagnosed late and disparities in access to HIV testing services remain. Point-of-care (POC) HIV tests are recommended when it is not feasible to conduct more sensitive laboratory-based HIV tests and can be useful in serving hard-to-reach populations. However, currently FDA-approved POC tests are less effective at identifying early and acute HIV infection, and antibody-based tests in particular can be affected by antiretroviral use for treatment or pre- exposure prophylaxis. Recent developments in HIV testing have potential to improve diagnosis during acute HIV infection; improve test performance in people taking antiretroviral medications for prevention and treatment; and distinguish between recent and longer-term infections to focus interventions on networks of ongoing transmission. Rigorous, comparative evaluations of the performance of the newest HIV tests in real world settings are needed to inform their use in clinical care, outreach, and other settings. The project proposed for this Cooperative Agreement will evaluate the diagnostic and clinical performance of the newest HIV testing technologies and establish panels of data and specimens for evaluations of laboratory-based tests. We will recruit people at high risk for HIV, taking antiretrovirals for prevention or treatment, with recent HIV infection, and people with HIV who are not taking ART or have not achieved viral suppression into a cross-sectional study to evaluate the relative sensitivity and specificity of the newest POC HIV tests compared to the CDC-recommended laboratory algorithm (Aim 1). Participants from Aim 1 with discordant tests will be recruited into a longitudinal study with frequent visits to evaluate the sensitivity of these tests during seroconversion (Aim 2). At study visits for Aims 1 and 2, we will also evaluate the diagnostic and clinical performance of POC nucleic acid tests (Aim 3) and collect matched demographic, behavioral, and clinical data to assess the impact of these factors on HIV test performance (Aim 4). Finally, specimens will be collected from participants and matched with their demographic, clinical, and behavioral data to support additional evaluations of laboratory-based HIV tests (Aim 5). Employing a research team with substantive experience in HIV testing including POC and nucleic acid tests, pre-exposure prophylaxis and HIV clinical care, HIV epidemiology, and public health programs and policy, this evaluation and comparison of the newest HIV testing technologies will inform HIV testing guidelines and support health care providers in deciding which tests to use in different settings and different populations.