A more complete picture
Genotypic testing detects mutations associated with antiretroviral resistance and utilizes interpretive algorithms to predict susceptibility of antiretrovirals (ARVs). Phenotypic testing provides a direct measure of drug susceptibility by quantifying the ability of ARVs to inhibit HIV reproduction in cell culture. The quantitative measure of drug susceptibility is compared with a wild-type, ARV-susceptible reference strain of HIV and translated to a Fold Change (FC) value.1
The combination of these two assays overcomes the limitations associated with genotypic or phenotypic testing alone. In cases of discordance between the two technologies, a net assessment, based on a proprietary, rules-based system, resolves the difference.
The addition of phenotypic to genotypic testing is noted in US Department of Health and Human Services (DHHS) guidelines as preferred for patients who may benefit from drug resistance testing due to known or suspected complex drug resistance patterns.2