I. Types of drug resistance testing methods HIV drug resistance testing can be done using both genotypic and phenotypic methods. We commonly use the genotypic method, which actually detects mutations in genes that cause phenotypic resistance or affect virological response, by using PCR methods to sequence amplification and sequencing for drug-acting target genes (e.g., reverse transcriptase or protease). Genotypic resistance testing begins by obtaining a specific gene fragment of the virus, determining the gene sequence, submitting the sequence to a selected database, and deriving a determination of drug resistance mutations and resistance by database matching, which typically yields results within 1-2 weeks. Phenotypic resistance testing is very complex and requires first obtaining a specific gene fragment of the virus, constructing a pseudovirus based on the patient’s genetic mutation, testing the ability of the constructed pseudovirus to replicate and grow in the presence of drugs, and comparing it to a wild strain to determine the degree of drug sensitivity or tolerance of the virus in the patient. Phenotypic drug resistance testing is demanding, cannot be done by general institutions, and is more difficult to popularize. B. When drug resistance testing should be performed 1. Newly diagnosed patients: Whether or not the patient will soon be on antiviral therapy is advocated for advanced drug resistance testing after diagnosis. It has been shown that drug-resistant HIV strains can be transmitted to patients who have received treatment, so that these patients acquire primary drug resistance from the beginning, known as transmission resistance. Transmission resistance is associated with treatment failure in patients, and resistance testing in such patients can help select the treatment regimen that will achieve the greatest viral suppression. 2. Patients receiving antiviral therapy: For patients receiving antiviral therapy who fail to respond virologically (HIV RNA > 1000 copies/ml) or who have unsatisfactory viral suppression when changing their antiviral regimen, drug resistance testing should be performed to determine whether drug resistance has occurred and to which drug, so as to guide the selection of active anti-HIV drugs for subsequent treatment. For patients with HIV RNA of 500-1000copies/ml, drug resistance testing is more difficult, but should still be performed as much as possible; for patients with <500copies/ml, drug resistance testing is not recommended. < span=""> 3. Pregnant women: All pregnant women should undergo genotypic resistance testing before starting ART. The goal of ART is to minimize plasma viral load and prevent mother-to-child transmission of HIV, with the primary goal of achieving maximum viral suppression. Therefore, genotypic drug resistance testing should be performed before starting antiretroviral therapy in pregnant women, and drug resistance testing should also be performed in pregnant women who have already received treatment and whose HIV RNA is still detectable. Drug resistance is only one of the possible causes of treatment failure and is closely related to other factors that contribute to treatment failure, including insufficient antiviral activity of drugs, poor compliance with medication and individual differences in pharmacokinetics. Therefore, drug resistance test results should not be viewed in isolation, but should be analyzed in the context of changes in viral load and CD4+ T lymphocyte count, clinical presentation, and changes in other tests. Resistance test results must be interpreted in the context of previous treatment history, long-term changes in plasma viral load, and the degree of adherence.