HIV-I Drug Resistance Assay (RT)

The HIV drug resistance test checks whether a person’s virus carries mutations that reduce effectiveness of antiretroviral drugs. Performed on a blood sample, the common genotypic test sequences viral genes to identify resistance mutations; phenotypic tests measure virus growth with drugs. It’s used at diagnosis, when treatment fails, or before switching therapy to guide drug choice and optimize viral suppression.

Do an HIV resistance test at baseline (at diagnosis) and before starting or changing antiretroviral therapy—including in pregnancy—to detect transmitted or prior resistance. Repeat testing after confirmed virological failure to guide regimen changes. Genotypic testing usually needs a sufficiently high viral load (commonly >500–1,000 copies/mL) for reliable results; seek specialist advice if viral load is lower or the case is complex.

HIV‑1 genotype "not detected" means the resistance test did not find HIV‑1 genetic sequences or drug‑resistance mutations. This commonly happens when viral load is too low for sequencing—often due to effective antiretroviral therapy—or because no resistance mutations are present. It does not mean the virus is cured. Discuss results with your clinician; repeat testing may be advised if viral load rises or treatment concerns persist.

A phenotype resistance assay for HIV is a laboratory test that measures how well a patient’s virus grows in the presence of antiretroviral drugs. It compares drug concentrations needed to inhibit the patient’s virus with a reference (wild-type) virus, reporting fold-change and susceptibility. It’s used when treatment fails or genotypic results are unclear, and is more direct but slower and costlier than genotypic testing.

Drug-resistant HIV has mutations that make one or more antiretroviral drugs less effective, risking treatment failure, rising viral load, falling CD4 counts and greater illness or transmission. Management uses resistance testing, switching to different drug classes or salvage regimens, close monitoring and specialist care. Newer agents can often suppress resistant virus, but adherence and regular follow-up are essential to prevent further resistance.

An HIV assay refers to tests detecting infection or monitoring disease. Screening uses antigen/antibody immunoassays (4th‑generation) that detect p24 antigen and HIV antibodies. Reactive results are confirmed with an HIV‑1/HIV‑2 differentiation immunoassay or nucleic acid test (NAT). NAT/PCR detects viral RNA for early diagnosis and measures viral load; CD4 count assesses immune system status.