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The diagnosis of autoimmune diseases is not straightforward, and requires a history, physical exam, laboratory testing, radiography, and sometimes biopsies.

Blood tests can be helpful, but often do not hold the complete answer. The most common blood test first ordered when an autoimmune disease is suspected is the antinuclear antibody test, otherwise known as the ANA. There are dozens of other tests, most of which involve the immune system, that try to detect autoimmunity.

Blood tests are only part of the workup, and by themselves do not give a diagnosis. Many people have a positive ANA, but have no autoimmune disease (referred to as testing falsely positive.) Other patients might have conditions such as rheumatoid arthritis, with normal blood work (referred to as testing falsely negative.)

Because of the high incidence of false positive and false negative blood test results, the diagnosis of autoimmune disease can be a process of careful history taking, examination, and observation over time.