Tetanus is a disease caused by the bacterium Clostridium tetani that enters the body through contaminated wounds. The bacterium is naturally present in soil, in animal and human intestines, in feces, etc. This test is to verify the effectiveness of the tetanus vaccination, especially if you are unsure when you were last inoculated.
This blood test doesn’t need to be on an empty stomach. There are no special preparations for this particular blood test.