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Lady Gaga told Larry King Tuesday that she has been tested and is “borderline” for lupus. In fact, she said, lupus runs in her family.

Gaga is well known for her theatrical stage performances. But this disease has real drama all its own, including its diagnosis.

Let’s break it down so that we all understand what lupus is and how the diagnosis process works.

Lupus is an inflammatory multisystem disease, the cause is unknown and its course is variable. Its occurs most often in women during the reproductive years and less commonly in men, children, and older women. The symptoms of lupus occur as a result of inflammation of the skin, joints, kidney, lungs, the nervous system and other body parts. The diagnosis is fairly straightforward if the patient has numerous physical and laboratory findings to support the diagnosis. Many folks, however, have vague symptoms such as fatigue or a rash or joint pain making it a bit harder to diagnose.

There are 11 or so criteria used for the diagnosis of systemic lupus erythematosus (SLE for short). Some of these criteria are blood tests (ANA, etc.) others include skin conditions or conditions such as arthritis and seizures. It’s diagnosed based on a number of physical findings and lab abnormalities.

While the exact cause or trigger to for lupus is unknown, genetics are thought to play a role because the disease tends to run in families. A person who develops lupus probably inherits the risk from one or both parents. They develop the disease, however, only after exposure to a still unidentified trigger, which could include sunlight, an infection, surgery, being pregnant or something else. It also involves an individual’s immune system. That’s because cells of the immune system play a key role in the inflammation that affects the entire body. The immune system mistakenly attacks normal cells and body organs leading to the manifestation of the disease.

Gaga says she is symptom free. We wish her all the best. Add your well-wishes on the WebMD Health Exchange.