HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes
- Screen for and confirm HIV-1/HIV-2 infection, including acute HIV-1 infection
- Differentiate HIV-1 from HIV-2 infection
IMPORTANT: NOTE THIS IS A REFLUX TEST - The price charged for this test is only for the HIV Antigen and Antibody, 4th Generation Screen in step 1 below. If this test is “reactive” then Quest automatically runs the HIV-1/2 Antibody Differentiation test and, an additional charge of $74 will be charged for this test. If the HIV-1/2 Antibody Differentiation is “indeterminate or nonreactive” then Quest automatically runs the HIV-1 RNA, Qualitative, TMA and an additional fee of $168 will be charged for this test.
Step 1 - Test HIV Antigen and Antibody, 4th Generation Screen is initially run
- Nonreactive then result is Negative and no further testing (HIV-Infection unlikely)
- Repeatedly reactive then Step 2
Step 2 - HIV-1/2 Antibody Differentiation (run if Step 1 is positive)
- Reactive then interpret test results as HIV Infection (HIV-1, HIV-2 or undifferentiated)
- Indeterminate or nonreactive then Step 3.
Step 3 - HIV-1 RNA, Qualitative, TMA (run if Step 2 is Indeterminate or Negative)
- Negative then result is Negative (false positive) and (HIV-1 infection unlikely. Consider testing for HIV-2 DNA if clinically indicated)
- Positive then interpret test results as Acute HIV-1 infection
This algorithm depicts the testing pathway of the HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes test. Although nonreactive results on the fourth-generation screening test and negative results on the HIV-1/HIV-2 differentiation test are consistent with an absence of infection, they may also represent samples collected before the development of detectable p24 antigen and HIV antibodies. Individual risk assessments may be helpful to determine the need for, and the frequency of, re-screening for patients with nonreactive/negative results.
The algorithm is provided for informational purposes only and is not intended as medical advice. A physician’s test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.
The HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes detects HIV p24 antigen in addition to HIV antibodies. Because HIV p24 antigen is detectable before seroconversion, fourth-generation assays can detect HIV-1 during acute infection; the inclusion of HIV-1 and HIV-2 antibodies allows detection after seroconversion, when p24 antigen becomes undetectable. Fourth-generation assays have >99.7% sensitivity and >99.3% specificity for HIV infection and can identify most (>80%) acute infections that would otherwise require nucleic acid testing for detection.6,7 In general, they can detect infection 0 to 20 days (median, 5-7 days) before third-generation immunoassays.5,8,9
Repeatedly reactive results on fourth-generation screening tests require confirmation with a supplemental test, such as an HIV-1/HIV-2 antibody differentiation assay. Differentiation between HIV-1 and HIV-2 antibodies can have treatment implications, as HIV-2 does not respond to some antiretroviral agents. Differentiation tests also tend to detect antibodies earlier than Western blots. HIV-1/HIV-2 antibody differentiation tests do not detect acute infection. HIV RNA testing is thus needed to resolve infection status in patients with positive results on the fourth-generation assay but negative results on the antibody differentiation test.