Resistance testing identifies drugs that should be avoided, but not necessarily the drugs that are most likely to be active.

Testing should be done in the presence of the antiretroviral agents in question, as discontinuation of therapy often results in the proliferation of wild type virus that could suggest susceptibility. The time between discontinuation of HAART and the shift from resistant strains to wild type virus is usually 2-8 weeks, though there is considerable variation depending on the specific mutation.

Interpretation of results in people who have received prior antiretroviral agents is difficult. Resistance to previously used drugs may be present even if resistance assays indicate susceptibility.

A viral load >500 to 1000 c/ml is usually required.

Results are more accurate with failure of early regimens.

genotype testing

phenotype testing