According to guidelines from the US Department of Health and Human Services (HHS), phenotypic resistance testing in addition to genotypic resistance testing is recommended for patients with known or suspected complex drug-resistance mutation patterns because phenotypic testing can provide additional useful information in patients with complex drug-resistance mutation patterns.
Drug resistance testing is recommended when changing ART regimens for patients with virologic failure and HIV RNA levels > 1000 copies/mL as well as for those with suboptimal viral load reduction. In patients with HIV RNA levels > 500 copies/mL but < 1000 copies/mL, drug resistance testing may not be successful, but it should still be considered. For patients with viral loads < 500 copies/mL, resistance testing is not usually recommended because it cannot be consistently performed at low HIV RNA levels.
Optimal prevention of perinatal HIV transmission requires prompt initiation of ART in HIV-positive pregnant women. Thus, ART initiation should not be delayed pending resistance testing results for pregnant patients. The ARV regimen can be changed as necessary once the results are received.
In the setting of virologic failure, drug resistance testing is recommended while the patient is taking prescribed ARV drugs or, when that is not feasible, within 4 weeks after discontinuing therapy. If more than 4 weeks have elapsed since the ARVs were discontinued, resistance testing may still provide useful information to guide therapy; however, it is important to recognize that previously selected resistance mutations can be missed owing to lack of drug-selective pressure at the time of testing.
Learn more about treatment-resistant HIV.
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Cite this: Michael Stuart Bronze. Fast Five Quiz: Treatment-Resistant HIV - Medscape - May 10, 2021.