Serologic tests are blood tests that look for antibodies in your blood. They can involve a number of laboratory techniques. Different types of serologic tests are used to diagnose various disease conditions. Antigens are substances that provoke a response from the immune system. They’re usually too small to see with the naked eye. They can enter the human body through the mouth, through broken skin, or through the nasal passages. Antigens that commonly affect people include the following: bacteria fungi viruses parasites The immune system defends against antigens by producing antibodies. These antibodies are particles that attach to the antigens and deactivate them. When the blood, is tested they can identify the type of antibodies and antigens that are in your blood sample, and identify the type of infection you have.