Test Details: Once a person gets HIV, the virus begins to multiply in the body. As HIV multiplies, it sometimes changes form (mutates). Some HIV mutations that develop while a person is taking HIV medicines can lead to drug-resistant HIV. Drug resistance testing is used to determine whether a patient with HIV has a mutated form of the virus that does not respond to antiretroviral therapy (ART). Genotypic resistance testing examines the genetic structure (genotype) of a patient's HIV. A blood sample is taken from the patient and the HIV is analyzed for the presence of specific genetic mutations that are known to cause resistance to specific drugs.