Lady Gaga told Larry King this week that she tested “borderline positive” for lupus, according to CNN.com. It sounds strange, but doctors confirm that this can happen with lupus, since the autoimmune disease is often hard to diagnose because of its vague and varying symptoms. No two cases are alike, according to medical experts. The disease can come and go without explanation, and its severity varies from mild discomfort to death.

According to WebMD, lupus is “an autoimmune disease, happens when the immune system attacks its tissues, causing inflammation, swelling, pain, and damage. Lupus symptoms vary, and early lupus symptoms include fatigue, joint pain, fever, and a lupus rash, especially after being in the sun.”

“Lupus is in my family, and it is genetic,” Lady Gaga said. “And it’s so funny because my mother told me the other day that my fans were quite worried about me because they did talk about the fact that I was tested for lupus. And the truth is I don’t show any signs, any symptoms of lupus. But I have tested borderline positive for the disease. So as of right now … I do not have it. But I have to take good care of myself.”

“There is not a single lab test that is specific for lupus,” said Dr. Gary Gilkeson, the vice chair of the department of medicine for research at the Medical University of South Carolina and the chair of the Lupus Foundation of America’s medical-scientific advisory council. “You have to use the combination of the lab tests plus the clinical signs and symptoms.”

“People with a family history can test positive, but never get it,” said Dr. Scott Zashin, clinical associate professor of medicine at the University of Texas Southwestern Medical School. “There is a little higher risk of developing lupus because of family history, but it’s possible to never get it.” Lady Gaga says her aunt died of lupus.

For more information, check out the Lupus Foundation of America.