Your immune system is part of your body’s defence system and plays an important role in keeping up your body’s resistance to disease-causing organisms. A healthy immune system can recognise foreign substances (known as antigens) and can develop proteins called antibodies which bind to the antigens and remove them from the body. Some of the cells that produce the antibodies remain as memory cells that can respond quickly and produce antibodies the next time that antigen invades the body.
These tests detect antigens or antibodies in the blood. They can be used to indicate the presence of e.g. viral infections such as Hepatitis B or HIV, bacterial infections e.g. Group A strep, syphilis, or to measure the level of immunity or resistance your body may have after vaccination e.g. rubella, hepatitis B.
Autoimmune disorders occur when your body loses its ability to tell the difference between its own tissue and foreign substances. In this case, the immune system attacks some of the body’s own tissues as if they were foreign. Blood samples can be taken to measure antibodies that your body may have produced against specific tissues. Blood tests for autoimmune diseases include Rheumatoid Factor (elevated in rheumatoid arthritis, where the immune system attacks the lining of some of the body’s joints) and Antinuclear Antibody test (elevated in systemic lupus erythematosus).
Immunodeficiencies result from defects in the immune system and can either be something you are born with or they can develop when you get an illness. Immune deficiencies very often lead to diseases such as recurrent bacterial infections, viral infections and autoimmune disease.