Genotypic antiretroviral drug resistance testing at low viral loads in the UK

Background: Antiretroviral drug resistance testing is recommended in HIV-1 infected patients failing therapy in order to inform treatment selection. Although guidelines and test manufacturers recommend a viral load of at least 500-1000 HIV-1 RNA copies/mL for genotypic resistance testing to be performed, prompt management of virological failure could benefit from testing at lower viral load levels. Methods: Laboratories undertaking genotypic resistance testing were asked to provide figures for the number of resistance tests undertaken at viral loads <2000 copies/mL, the success rates of such tests and the extent of resistance detected, all stratified for viral load levels. Results: Of the replies received, most laboratories were attempting resistance testing at viral loads below the recommended guidelines, with variable success and outcomes. Conclusions: This audit of current practice in the UK for undertaking genotypic resistance tests at viral loads <1000 copies/mL highlights the widespread use of such testing outside the British HIV Association guidelines