The following factors affect test results:

1. History of previous infection by the same organism

2. Previous vaccination (determine time frame)

3. Anamnestic reactions caused by heterologous antigens: An anamnestic reaction is the appearance of antibodies in the blood after administration of an antigen to which the patient has previously developed a primary immune response

4. Cross-reactivity: Antibodies produced by one species of an organism can react with an entirely different species (e.g., Tularemia antibodies may agglutinate Brucella, and vice versa, rickettsial infections may produce antibodies reactive with Proteus OX19)

5. Presence of other serious illness states (e.g., lack of immunologic response in agammaglobulinemia, cancer treatment with immunosuppressant drugs)

6. Seroconversion: The detection of specific antibody in the serum of an individual when this antibody was previously undetectable