When should testing for HBsAg and antibody HBsAg in infants ideally be performed?

Testing for HBsAg (Hepatitis B surface antigen) and antibody HBsAg (antibody to Hepatitis B surface antigen) in infants is ideally performed at 9 to 12 months of age to ensure accurate assessment of their Hepatitis B status. This timing is essential because it allows for appropriate evaluation after the natural immunity that infants may have received through maternal antibodies has waned.

Children who are born to mothers who are Hepatitis B positive may have maternal antibodies present early in life, which can interfere with the detection of the infant's own immune response. By testing at 9 to 12 months, clinicians can obtain a clearer picture of whether the infant has been infected or if they have successfully developed immunity from vaccination.

This age range aligns with both the CDC guidelines and the recommendations from the World Health Organization regarding the timing of Hepatitis B serology testing. Waiting until this age helps ensure that any vaccination the infant may have received has had enough time to elicit a measurable immune response, thereby providing more reliable results.