Successful use of genotypic resistance testing in HIV-1-infected individuals with detectable viraemia between 50 and 1000 copies/ml.

Traditionally an HIV viral load of over 1000 copies/ml was presumed necessary for genotypic resistance testing. We performed a retrospective analysis to assess rates of viral amplification on viral loads between 50 and 1000 copies/ml. Amplification was significantly more likely for 200-1000 copies/ml than 50-200 copies/ml; most samples amplified successfully, supporting the use of genotyping for low-level viraemia.