A positive antinuclear antibody (ANA) test does not automatically mean you have lupus. Your immune system is your body's natural defense against disease. A positive ANA blood test shows that your immune system is making an antibody (protein) that reacts with components of your body's cells. This is called autoimmunity and may or may not be harmful to your body. So while a positive ANA may be associated with an autoimmune illness like lupus, it does not mean you have the disease. Approximately 20% of the normal population will have a positive ANA test; positive tests are also seen in other conditions, such as thyroid disease, certain liver conditions, and other autoimmune diseases.