What it measures: HIV can mutate to become resistant to drugs. Resistance testing helps identify the meds that still work against HIV when others fail—or the meds you might not benefit from before you start treatment.
When it’s used: Before treatment is started (to see if you were possibly infected with drug-resistant HIV), when viral load increases while on treatment and when choosing meds to use during pregnancy. Genotyping and phenotyping tests are both available. Those with complex treatment histories might benefit from both tests.
Test Tip: The test can miss drug-resistant virus if the amount of HIV in your bloodstream is small (a viral load below 1,000). For best results, have blood drawn for the test before stopping or switching your treatment. If you haven’t started treatment, testing is best if only a few years have passed since the time of infection.
