Clinical Information

Seroconversion typically occurs 6–12 weeks after exposure, and HIV-1/2 antibodies are almost always detectable by 12 months. In late-stage AIDS, antibody levels may decline (seroreversion), but HIV p24 antigen is often detectable and will yield reactive results with combination antigen–antibody assays.

The Geenius HIV 1/2 Supplemental Assay is an immunochromatographic test used to confirm and differentiate antibodies to HIV-1 and HIV-2 in serum specimens. It is performed only on samples that are repeatedly reactive on an initial HIV-1/2 antigen/antibody screening assay. This test aids in the diagnosis of HIV-1 and/or HIV-2 infection but is not a screening assay and is not used for blood donor testing.

Clinical use

Confirms the presence of antibodies to HIV-1 and/or HIV-2 after a reactive screening test. Can be used in pediatric patients ≥2 years of age. Helps determine whether reactivity on the initial screen represents HIV-1 infection, HIV-2 infection, cross-reactivity, or an indeterminate pattern.

Interpretation of results

HIV-1 Positive

• Indicates confirmed antibodies to HIV-1.
• Recommendation: For first-time positive results, verify infection with a newly collected specimen or HIV-1 RNA testing.

HIV-2 Positive

• Indicates confirmed antibodies to HIV-2.
• Recommendation: For first-time positive results, repeat testing on a new specimen or perform HIV-2 RNA testing (where available) to verify diagnosis.

HIV-1 and HIV-2 Positive (Dual Reactivity)

• Dual reactivity may reflect:
• HIV-1 infection with HIV-2 cross-reactivity (common),
• HIV-2 infection with HIV-1 cross-reactivity, or rare dual infection.
• Recommendation: Verify using both HIV-1 and HIV-2 RNA testing.

Negative or Indeterminate

• A negative or indeterminate antibody differentiation result does not exclude early HIV infection.
• Laboratory action: Reflex HIV-1 RNA (PCR) testing will be performed automatically to rule out acute infection.

HIV-1 Positive / HIV-2 Indeterminate

• Antibodies to HIV-1 are confirmed.
• The HIV-2 indeterminate pattern is typically due to cross-reactivity, not HIV-2 infection.

HIV-1 Indeterminate / HIV-2 Positive

• Antibodies to HIV-2 are confirmed.
• The HIV-1 indeterminate pattern is usually due to cross-reactivity.

Important clinical considerations

• This assay confirms antibody reactivity only.

• Antibody formation may take several months to reach detectable levels after exposure.
• Diagnosis of HIV disease requires clinical correlation.
• False-negative antibody results may occur in people receiving ART, PEP, or PrEP, or during very early infection.
• A negative or indeterminate differentiation result after a reactive screen should be followed by HIV-1 RNA testing to exclude acute infection.
• HIV-1 and HIV-2 share significant homology; cross-reactivity is common, especially in HIV-2 infection.
• Rarely, specimens may be labeled HIV Positive Untypable, meaning HIV-2 infection with strong HIV-1 band reactivity cannot be distinguished.
• Individuals who have received HIV vaccines may have detectable antibodies without infection.

Testing algorithm

1. HIV-1/2 Antibody Differentiation Test
   • If negative for both HIV-1 and HIV-2 antibodies, or indeterminate, HIV-1 RNA detection is performed automatically (additional charge).
   • RNA testing is indicated for:
   • Negative for both HIV-1 Ab and HIV-2 Ab
   • Indeterminate HIV-1 Ab with negative HIV-2 Ab
   • Negative HIV-1 Ab with indeterminate HIV-2 Ab
   • Indeterminate for both HIV-1 Ab and HIV-2 Ab
2. When HIV-1 RNA Testing Is Recommended (Provider-Ordered)
   • Positive for both HIV-1 and HIV-2 antibodies
   • First-time HIV-1 positive
   • First-time HIV-2 positive