Effective Monday, October 18, 2010, the University of Iowa Hospitals and Clinics core Clinical Chemistry laboratory will begin running the Abbott Diagnotics' HIV Antigen/Antibody (Ag/Ab) Combo, an automated FDA-approved assay that detects both antigen and antibody in patients infected with either HIV-1 (group M and O) or HIV-2. The Combo assay will be available in Epic as "HIV ANTIGEN/ANTIBODY COMBO" [Epic LAB7444]. For antigen detection, the assay uses monoclonal antibodies directed against a highly conserved p24 peptide sequence of HIV-1 and HIV-2.

A positive Combo assay indicates either acute or chronic infection with HIV-1 and/or HIV-2. Relative to other HIV screening tests such as ELISA or OraQuick that detect antibodies against the virus, the Combo assay shortens the "serological window", reducing the chance of a false-negative result in a patient who has not yet produced enough antibodies to be detected with ELISA or other tests for anti-HIV antibodies.

The antigen-antibody combination tests are designated "fourth-generation" HIV tests and have been available in Europe for nearly a decade, and are now considered standard of care in Great Britain, France, and Germany. The Centers for Disease Control and Prevention (CDC) has actively worked since 2007 to encourage the marketing of fourth-generation HIV tests in the United States. The Combo assay will be available 24/7, 365 days a year (including holidays) with a turnaround time of one hour or less after specimen receipt in the laboratory (matching the turnaround time of the OraQuick rapid HIV test). The Combo assay will replace the following tests that will be discontinued:

     "HIV 1/2 ANTIBODY" [Epic LAB629] (send-out test to reference laboratory using ELISA with positives
      reflexed to Western blot)

     "RAPID HIV1/2" [Epic 5747] (OraQuick rapid assay performed in core laboratory, often used in work-up
      of healthcare worker exposure to potentially infectious body fluids such as occurs in needlestick injury)

Epic order sets that contain either of the above two tests will be updated to have "HIV ANTIGEN/ANTIBODY COMBO". All positive assay results will be confirmed with Western blot ("HIV 1 ANTIBODY, CONFIRMATION").

Like many other HIV screening tests (including ELISAs), the Combo assay is not approved for children less than two years old. For HIV screening in children less than two years, PCR testing is often used. Consultation with pediatric infectious disease specialists is recommended if unsure about testing approaches in children less than two years old.

Other HIV tests currently available including "HIV QUANTITATIVE PCR" [Epic LAB2468, "viral load"], "HIV-1 RNA genotyping" [Epic LAB5745, for detecting antiretroviral resistance], and "HIV-1 PROVIRAL DNA, QUAL PCR" [Epic LAB3339, often used in neonates and infants] will continue to be available.

Questions should be directed to Matthew Krasowski, MD, PhD, medical director of the Clinical Chemistry
(384-9380, matthew-krasowski@uiowa.edu).