HIV testing programmes need to ensure that all clients who test for HIV are provided with correct diagnoses. The accuracy of HIV testing is critical to prevent misdiagnosis, as the consequences of giving an incorrect test result can be serious for clients, HIV testing services, HIV programmes and public health. With the evolution of global HIV epidemiology, HIV testing approaches must also evolve to maintain accuracy and efficiency in population-level diagnosis. Reports suggest that misdiagnosis of HIV status may occur when suboptimal testing algorithms and out-of-date testing strategies are used. As a result of changing epidemiology and declining HIV positivity in testing, WHO recommends all countries use a standard three-test strategy to ensure a PPV of at least 99%, minimizing false-positive misdiagnosis. The WHO-recommended HIV testing strategy, along with quality assurance measures such as retesting to verify a positive diagnosis prior to initiation of HIV treatment, is cost-effective as it prevents misdiagnosis and unnecessary initiation of costly lifelong treatment. This implementation guide provides practical advice on switching to a three-test strategy and instituting other measures that can help national HIV programmes deliver high-quality, accurate HIV testing services and ensure that misdiagnosis is minimized.