http://resources.lupus.org/entry/how-lupus-is-diagnosed

How lupus is diagnosed: An overview

Lupus Foundation of America

Resource Content

In lupus, something goes wrong with your immune system, the part of the body that fights off viruses, bacteria, and germs. 

Normally, our immune system produces proteins called antibodies that protect the body from these foreign invaders. When you have lupus, your immune system cannot tell the difference between these foreign invaders and your body’s healthy tissues, so autoantibodies are made that damage and destroy healthy tissue (auto means self and anti means against, so autoantibody means against self). These autoantibodies cause inflammation, pain, and damage in various parts of the body.

A doctor who is considering the possibility of lupus will look for signs of inflammation which include, pain, heat, redness, swelling, and loss of function at a particular place in the body. Inflammation can occur on the inside of your body (your kidneys or heart, for example), on the outside (your skin), or both.

There are many challenges to reaching a lupus diagnosis. The disease is known as "the great imitator" because its symptoms mimic many other illnesses. The symptoms of lupus can also be unclear, come and go, or change over the course of the disease.

A physician will review the following while evaluating a lupus diagnosis:

  • Your current symptoms.
  • Your laboratory test results.
  • Your medical history.
  • The medical history of your close family members (grandparents, parents, brothers and sisters, aunts, uncles, cousins).

There is no single diagnostic test for systemic lupus. The test you will hear most about is called the antinuclear antibody (ANA) test. This is not a specific test for lupus, however. In fact, a variety of laboratory tests are used to detect physical changes or conditions in your body that can occur with lupus. Each test result adds more information to the picture your doctor is forming of your illness.

Laboratory tests alone cannot give a definite “yes” or “no” diagnosis because of the following limitations:

  • No single laboratory test can determine whether a person has lupus.
  • Test results that suggest lupus can be due to other illnesses or can even be seen in healthy people.
  • A test result may be positive one time and negative another time.
  • Different laboratories may produce different test results.

If multiple diagnostic criteria are present simultaneously, your physician may reach a lupus diagnosis. If, however, as is often the case, symptoms present gradually over time, the diagnosis may not be as obvious. In these cases, further consultation with a rheumatologist may be needed.

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