Lupus is chronic and complex, and is often difficult to diagnose.
There is no single laboratory test that can determine if a person has lupus.
To complicate matters, many symptoms of lupus are similar to those of other diseases, and can come and go over weeks and months. It can often take years for a diagnosis to be made.
To diagnose lupus, a doctor should be able to find physical or laboratory evidence of the condition, such as swelling of joints, protein in the urine, fluid around the lungs or heart, or a skin biopsy (test of a sample) that shows evidence of the disease. The doctor also will look at a person’s medical history and special tests to rule out other diseases.
Doctors use the American College of Rheumatology's “Eleven Criteria of Lupus” to help make—or exclude—a diagnosis of lupus.
Typically, four or more of the following criteria must be present to make a diagnosis of systemic lupus.
The “Eleven Criteria”
- Malar rash: butterfly-shaped rash across cheeks and nose
- Discoid (skin) rash: raised red patches
- Photosensitivity: skin rash as result of unusual reaction to sunlight
- Mouth or nose ulcers: usually painless
- Arthritis (nonerosive) in two or more joints, along with tenderness, swelling, or effusion. With nonerosive arthritis, the bones around joints don’t get destroyed.
- Cardio-pulmonary involvement: inflammation of the lining around the heart (pericarditis) and/or lungs (pleuritis)
- Neurologic disorder: seizures and/or psychosis
- Renal (kidney) disorder: excessive protein in the urine, or cellular casts in the urine
- Hematologic (blood) disorder: hemolytic anemia, low white blood cell count, or low platelet count
- Immunologic disorder: antibodies to double stranded DNA, antibodies to Sm, or antibodies to cardiolipin
- Antinuclear antibodies (ANA): a positive test in the absence of drugs known to induce it. A special note on the ANA test
Other Types of Lupus
Although the broad term "lupus" usually refers to Systemic Lupus Erythematosus or S.L.E., this is only one type of lupus. Other types of lupus are:
- Cutaneous or “skin” lupus erythematosus. This form of lupus mainly affects the skin—not the rest of the body. Signs include a rash on the face, scalp, or elsewhere that may last for days or years, and can recur. Unlike systemic lupus, cutaneous lupus does not threaten the health of other organs and tissues in the body. And although it’s clearly a concern, it’s not that common for cutaneous lupus to turn into systemic lupus. A type of cutaneous lupus called “discoid” lupus involves potentially scarring sores with inflammation, typically on the face, scalp, and ears. These lesions can scar.
- “Drug-induced lupus” is triggered by the use of certain medicines. It usually goes away once the triggering medicines are stopped. Symptoms of this form of lupus are often relatively mild.