Diagnosing lupus can be a difficult and time-consuming process because its symptoms frequently mimic those of other diseases. Joint pain can be a sign of other forms of arthritis, while fatigue leads people to believe that they are simply stressed or overworked.
Because lupus symptoms wax and wane, it can be difficult for doctors to make a definite diagnosis. For example, while the butterfly rash often is considered the hallmark of lupus, many patients never experience it.
If a primary care doctor suspects lupus, he may provide a referral to a rheumatologist, a doctor who specializes in autoimmune diseases.
The rheumatologist will ask questions about symptoms, including how and when they started, if they come and go, how severe they are and if anything makes them better or worse. A physical examination will be done to thoroughly check the joints, skin, lungs, nerves and blood vessels.
Different laboratory tests are done to tests are ordered to rule out other conditions and help diagnose lupus. They include:
- Complete blood count (CBC). A CBC checks the levels of red blood cells, white blood cells and platelets (blood cells that help to control bleeding and clotting).
- Blood chemistry and urine tests. These can help determine whether organs, such as the kidneys and liver, are working properly.
- Biopsy. A biopsy is the removal of a small piece of tissue from the affected area. For lupus, the sample is taken from a rash or from the kidney when symptoms are active. It can help definitively diagnose the disease.
- Anti-nuclear antibody (ANA) blood test. This detects a group of proteins (called autoantibodies) found in the blood of people with lupus. While this test alone does not diagnose lupus, it can help confirm a diagnosis.
- Antibody testing. If the ANA test is positive, the doctor may order other specific antibody tests. Antiphospholipid antibodies, including cardiolipin, are common in lupus. They are associated with an increased risk for blood clotting, strokes and recurrent miscarriages.
- Complement proteins. This blood test measures the level of complement proteins in the blood. People with lupus often have reduced levels of complement, which can indicate active lupus.
- Erythrocyte sedimentation rate (ESR, or “sed rate”) and C-reactive protein (CRP). Both of these levels are markers for inflammation. A high ESR or CRP combined with other signs of lupus can help make a diagnosis and assess disease activity.