Cautions

Due to the complexity of the results generated, the International AIDS Society-USA Panel recommends expert interpretation of genotyping and phenotype test results for patient care management. A patient's response to antiviral therapy depends on multiple factors, including the percentage of patient's viral populations that is drug resistant, patient compliance with the prescribed drug therapy, patient access to adequate care, drug pharmacokinetics, and drug interactions. Drug resistance test results should be interpreted only in conjunction with clinical presentation and other laboratory markers when making therapeutic decisions.

Absence of resistance to a drug does not rule out the presence of reservoirs of drug-resistant virus in the infected individual.

The HIV-1 genotypic test is not a direct measure of drug resistance. Although genotypic testing can detect variants in the relevant HIV-1 genome, the significance of these variants requires careful interpretation to predict drug susceptibility. This assay's ability to amplify the target and detect genotypic mutation is poor and unreliable when the plasma HIV-1 viral load (VL) is less than 1000 copies/mL. Specimens submitted for this test should contain greater than or equal to 1000 copies/mL of HIV-1 RNA. Per assay manufacturer claims, the assay's ability to detect minor drug-resistant HIV-1 variants among 90% or more of HIV-1 group M strains varies depending on the VL in the tested plasma specimen; 20% or higher at VL of 1000 copies/mL, 10% or higher at VL of 5000 copies/mL, and 5% or higher at VL of 15,000 copies/mL.

The list of drug resistance-associated codon mutations and interpretive rules used by the Stanford HIV database are updated periodically by the Stanford HIV Database team. Therefore, the test results do not necessarily include all resistance-associated codon mutations described in the current medical literature.

Possible causes of treatment failure other than the development of drug resistance are poor adherence to medication regimen, drug potency, and individual variation in pharmacokinetics (eg, inadequate phosphorylation of nucleosides).