As you probably know, the hepatitis B vaccine is a series of three shots that are given over a period of several months to produce immunity to the hepatitis B virus. The vaccine is effective in those who respond to it, however a small but significant proportion of people who receive the vaccine will not produce detectable antibody levels in their blood stream after receiving the vaccine and, therefore, might not be immune to the virus.
Therefore, in situations where it is important to document immunity, it is common to draw a blood test looking for antibodies after completing the vaccinations. This test specifically tests antibodies to the hepatitis B surface antigen. It is not generally reported as the "exact" antibody level, but rather as positive or negative. If positive, the person is immune to the hepatitis B virus. If, on the other hand, the test is negative then the person is one of those who did not respond adequately to vaccination, and they may need to have a booster dose of the vaccine.
Your wife should talk to her primary care doctor
about this issue. They can order the necessary blood tests to determine whether or not she has immunity to hepatitis B.