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The doctor will ask about your symptoms and medical history, and perform a physical exam. Lupus is first suspected on the basis of symptoms, especially if you are a young woman. A firm diagnosis of lupus is somewhat complicated and will require a great deal of information and the consultation of a specialist. This is because lupus has no identifiable cause and no single definitive test. Also, since lupus can affect many systems in the body, it does not show the same signs and symptoms in everyone.

In 1982 the American College of Rheumatology decided on a set of criteria that yields an accurate lupus diagnosis 98% of the time. This diagnosis requires that you have at least four of the following:

• Typical (malar) facial rash
• Typical (discoid) rash on sun-exposed areas
• Skin photosensitivity (easily burned by the sun)
• Ulcers in the mouth or above the back of it (the nasopharynx)
• Arthritis in at least two limb joints—meaning that a joint is painful, swollen, warm, and red, not just painful
• Inflammation of the lining of the heart or lungs (serositis)
• Kidney abnormalities—identified by kidney function tests (For example, protein in the urine is a sign that the kidneys are affected.)
• Seizures or psychosis
• Abnormally low number of blood cells—determined by a blood test called a complete blood count (CBC)
• Antinuclear antibodies—This is determined by a specific lab test. Nearly all people with lupus test positive for these antibodies. They are immune chemicals produced by your body that attack the contents of the nuclei of your body's cells. These antibodies are believed to contribute to the cause of lupus.
• Immune dysfunction—In people with lupus, several other antibodies have been found. These antibodies can be detected with specific lab tests.