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

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.

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.

Of the replies received, most laboratories were attempting resistance testing at viral loads below the recommended guidelines, with variable success and outcomes.

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.