Final answer:
An Antibody/Antigen test, often a fourth-generation test that can detect both HIV antibodies and p24 antigen, is typically the first administered for suspected HIV infection. It is confirmed by follow-up tests such as the Western blot or PCR (polymerase chain reaction).
Step-by-step explanation:
The first test usually administered to a patient with high risk or presenting symptoms of HIV is typically an Antibody/Antigen test, which includes fourth-generation tests that can detect HIV antibodies and HIV p24 antigen. These are often referred to as "combo" tests and provide a benefit in that they can identify HIV infections during the acute phase, which is before the body has fully mounted an antibody response. Conventional tests, such as an ELISA test, are widely used and work by detecting anti-HIV antibodies that would bind to the HIV peptides attached to a well in a 96-well plate. Positive results from initial tests are confirmed with follow-up tests like the Western blot or nucleic acid tests (NATs), which can detect the viral load or the presence of the virus in a patient's blood, although NATs are less commonly used due to their high cost.