A newborn positive for toxoplasma IgG. To confirm active infection, which test would be used?

A newborn positive for toxoplasma IgG. To confirm active infection, which test would be used?

• A. Maternal IgG
• B. Newborn IgM
• C. Maternal IgM
• D. Newborn IgG

Answer: (B)

When a newborn tests positive for toxoplasma IgG, that result can reflect antibodies the mother passed to the baby across the placenta rather than a true fetal infection. To confirm active congenital infection, you look for the baby’s own immune response. The presence of toxoplasma-specific IgM in the newborn indicates the fetus produced antibodies in response to infection, since IgM does not cross the placenta. This makes the test for newborn IgM the best way to confirm active infection. Maternal IgG just shows transferred antibodies, maternal IgM signals maternal infection but doesn’t prove the infant is infected, and newborn IgG would largely be maternal IgG as well.

When a newborn tests positive for toxoplasma IgG, that result can reflect antibodies the mother passed to the baby across the placenta rather than a true fetal infection. To confirm active congenital infection, you look for the baby’s own immune response. The presence of toxoplasma-specific IgM in the newborn indicates the fetus produced antibodies in response to infection, since IgM does not cross the placenta. This makes the test for newborn IgM the best way to confirm active infection. Maternal IgG just shows transferred antibodies, maternal IgM signals maternal infection but doesn’t prove the infant is infected, and newborn IgG would largely be maternal IgG as well.