Today's drugs are not completely able to stop HIV from reproducing. If a resistant virus develops, it can grow in the presence of the drug and viral load subsequently starts to rise. Drug-resistant virus will grow more quickly and become the most prominent virus in a person's blood. Lab tests can show whether a person's virus is likely to be suppressed by each anti-HIV drug. There are two different types of resistance tests.
Genotypic tests look for genetic mutations that have been linked to drug resistance.
Phenotypic tests assess which drugs can stop HIV growing in a lab setting. To accurately measure drug resistance, people should be on anti-HIV drugs and have a viral load of over 1,000 copies. Otherwise, the results may not be accurate or the test cannot be performed. Current anti-HIV drugs target one of two vital HIV genes or proteins. Genotypic tests look for mutations in the genes for these drug targets.