A postvaccination test for immunity to the hepatitis B virus (HBV) is recommended only if you:

• Have an impaired immune system. This can be caused by many conditions, such as infection with HIV or the use of medicines to prevent organ rejection.
• Are older than age 49.
• Received the hepatitis B vaccine in the buttock. (The vaccine is less effective when given in the buttock. It is more effective when given in the upper arm.)
• May come in contact with other people's blood or body fluids as part of your job.
• Are a sex partner of someone with chronic hepatitis B virus infection.

Infants born to mothers who are infected with HBV should be tested at 9 to 15 months of age.

With the exception of infants, a postvaccination test for immunity should be done between 1 and 2 months after a person receives the last dose of vaccine.