HIV testing and monitoring

Abstract

There is a broad range of tests used for HIV screening, diagnosis of infection, monitoring disease progression and response to therapy. Viral replication occurs during the incubation period, during which the viral genome and, briefly, viral p24 antigen may be detected. HIV diagnostic tests can be divided into combined antibody and antigen detection, antigen detection, antibody detection and genome detection. An HIV test is performed after pre-test counselling. If HIV antibody has been detected, the result must be confirmed by testing the unseparated sample and then on a further sample to ensure that no procedural error has occurred. Quantification of plasma HIV-1 RNA (‘HIV load test’) should be part of the baseline tests when the second sample is collected. The impact of highly active antiretroviral therapy (HAART) on HIV disease progression has been significant. In the UK, the incidence of AIDS and AIDS-related death has decreased by more than 40% since 1996. Emergence of drug-resistant virus and variable compliance in taking HAART lead to failure of treatment. Antiviral drug resistance occurs when the susceptibility of the virus to specific antiviral drugs is reduced. Specific mutations in the viral reverse transcriptase and protease genes have been identified, are associated with reduced drug susceptibility and can be detected by nucleic acid sequencing of plasma virus. These genotypic resistance tests are used increasingly in a routine capacity. In addition, phenotypic assays can be used to detect resistance, which is expressed as fold reduction in drug susceptibility compared with a wild-type (drug-sensitive) strain.