Antiretroviral Resistance Testing

Genotypic analysis examines viral genes that encode reverse transcriptase, protease, and integrase. The laboratory looks for resistance-associated mutations within these regions, then relates the detected pattern to susceptibility to particular antiretroviral drugs. This matters because HIV variants can differ in their treatment response, allowing clinicians to avoid relying only on a standard regimen when the viral sequence indicates reduced susceptibility.

Phenotypic testing measures the extent to which different drug concentrations inhibit viral replication, whereas genotypic testing uses resistance-associated mutations in viral genes to assess susceptibility. The phenotypic approach therefore supplies a drug-response measurement rather than a mutation profile. Used alongside sequence-based information when appropriate, it can clarify how a viral variant behaves against specific antiretroviral options.

Resistance testing is useful in virologic failure because it can show whether reduced treatment response is associated with resistant HIV variants. A result that does not indicate resistance helps clinicians consider that failure may have another explanation, rather than assuming drug resistance is responsible. This distinction supports more targeted treatment decisions and prevents resistance findings from being interpreted in isolation.

The workflow centers on choosing the measurement that addresses the clinical question. For genotypic analysis, viral genes such as those encoding reverse transcriptase, protease, or integrase are sequenced to identify resistance-associated mutations. For phenotypic analysis, inhibition of viral replication is measured across drug concentrations. The resulting susceptibility information can then inform regimen selection or evaluation of treatment failure.

Testing can inform both initial regimen selection and evaluation after virologic failure. In the first setting, resistance findings can help match therapy to the susceptibility profile of the HIV variant. In the second, they can clarify whether resistance is contributing to poor viral control. This dual use makes the approach relevant to individualized HIV care across different treatment decisions.

It contributes to surveillance of transmitted and acquired drug resistance, extending the value of laboratory findings beyond a single treatment decision. Genotypic mutations and phenotypic susceptibility measurements connect observed viral characteristics with patterns of resistance in HIV. This broader context helps relate individual test results to ongoing monitoring of viral evolution and therapeutic effectiveness.