HIV Ab and Ag combination

Keywords: HIV antibody and antigen, HIV antibody/antigen, HIV antibody, HIV antigen

Specimen:

10 mL of blood in a plain tube. Informed consent must be obtained from the patient, prior to ordering the test.

Method:

Immunoassay for detection of both HIV-1 and HIV-2 antibodies and HIV p24 antigen. Specialised laboratories confirm positive immunoassay results by immunoblot methods.

Reference Interval:

Positive is significant, if confirmed by HIV antigen assay for p24 or immunoblot for antibodies.

Application:

Diagnosis of HIV infection. Screening of blood, tissue or organ doners. Following exposure, the seronegative "window" period may be from 3 weeks to several months. Use of the combination assay decreases the time to detection of recent infection by 3 - 5 days compared with assays for antibodies alone. Occasional subtypes of HIV may be undetectable by some assays.

Interpretation:

Positive indicated HIV infection and must be confirmed by immunoblot or p24 assay and by testing on a separate sample. False positives are rare, and can be further assessed by immunoblot, tests for HIV antigen or, preferably, HIV-1 RNA and repeat HIV antibody testing; see HIV p24 antigen, HIV-1 RNA. In terminal disease, HIV antibodies may be negative. HIV-1 is common worldwide; HIV-2 is less common and is largely confined to Africa.

Patients where there is a high clinical suspicion and are negative for HIV antibody should undergo p24 antigen testing of Proviral DNA assay.