Why might an HIV test be positive in an infant born to an HIV-infected mother for up to 18 months?

Why might an HIV test be positive in an infant born to an HIV-infected mother for up to 18 months?

• A. Maternal antibodies crossing the placenta
• B. The infant is infected with HIV
• C. The test is inherently unreliable in infants
• D. Vaccination with live-virus vaccine

Answer: (A)

Maternal antibodies crossing the placenta is enough to cause this positive result in infancy. When a mother has HIV, she makes HIV antibodies that can pass into the baby through the placenta. Those maternal IgG antibodies can stay in the infant’s blood for many months, commonly up to about 12–18 months. Because antibody tests detect antibodies, not the virus itself, they can be positive in the baby even if the infant is not infected. To determine whether the infant actually has HIV, tests that detect the virus or its genetic material are used (such as HIV RNA or HIV DNA PCR) rather than antibody tests. Vaccination with live-virus vaccines would not cause an HIV antibody test to be positive in this context.

Maternal antibodies crossing the placenta is enough to cause this positive result in infancy. When a mother has HIV, she makes HIV antibodies that can pass into the baby through the placenta. Those maternal IgG antibodies can stay in the infant’s blood for many months, commonly up to about 12–18 months. Because antibody tests detect antibodies, not the virus itself, they can be positive in the baby even if the infant is not infected. To determine whether the infant actually has HIV, tests that detect the virus or its genetic material are used (such as HIV RNA or HIV DNA PCR) rather than antibody tests. Vaccination with live-virus vaccines would not cause an HIV antibody test to be positive in this context.