Systemic Lupus Erythematosus
DescriptionAn in-depth report on the causes, diagnosis, treatment, and prevention of Lupus.
Alternative NamesCorticosteroids; Immunosuppressant Drugs
The first symptoms of SLE can resemble one of many syndromes or disorders, including rheumatoid arthritis, Still's disease, rheumatic fever, Lyme disease, multiple sclerosis, thrombotic thrombocytopenia purpura, cryoglobulinemia, Weber-Christian disease, viral infections, vasculitis, psychosis, and other conditions. Other autoimmune disorders, such as Sjogren's syndrome or scleroderma, may even be present as a co-condition. No single test can definitively confirm or rule out SLE and a number are required before SLE can be diagnosed definitively.
Ruling out Other Conditions
The physician should first rule out common conditions that might be causing the symptoms. The physician may, for example, test the synovial fluid (the lubricating liquid surrounding joints) to rule out rheumatoid arthritis. Certain eye and saliva tests may be used if Sjgren's syndrome is suspected.
Tests for Autoantibodies
Methods for measuring the antibodies involved with SLE vary and the range of results can be bewildering. Repeat tests may be needed.
Antinuclear Antibodies (ANAs). One test is used to detect antinuclear antibodies (ANA), which attack the cell nucleus.
High levels of ANA are found in more than 98% of SLE patients. A number of other conditions, however, also cause high levels of ANA, so a positive test is not a definite diagnosis for SLE:
A negative ANA test makes a diagnosis of SLE unlikely but not impossible. High or low concentrations of ANA also do not necessarily indicate the severity of the disease, since antibodies tend to come and go in SLE patients.
In general, the ANA test is considered a screening test:
ANA Subtypes. In some cases, physicians may test for specific ANA subtypes.
Antibodies to SR Proteins. An advance in diagnosing SLE has been the detection of antibodies to molecules called SR proteins, which are carried by most patients. The test accurately detects lupus in 50% to 70% of patients who test positive for these antibodies.
Antiphospholipid Antibodies. In SLE patients in whom blood abnormalities are suspected, tests will be administered to detect the presence of the two major antiphospholipid antibodies:
As with the ANA, these antibodies also have a tendency to appear and disappear in a single patient. Patients who have these autoantibodies as well as blood clotting problems or frequent miscarriage are diagnosed with antiphospholipid syndrome (APS), which often occurs in SLE but can also develop independently.
Miscellaneous Blood Tests
Complement. Blood tests of SLE patients often show low levels of serum complement, a protein in the blood that aids the body's infection fighters. Individual proteins are termed by the letter "C" followed by a number; common complement tests measure C3, C4, C1q, and CH50. There is some evidence that complete deficiencies of C1q may be a key factor in the inability of the immune system to contain the autoimmunity process. Complement levels are especially low if there is kidney involvement or other disease activity.
LE Cell Tests. The first blood test ever used for SLE called LE (lupus erythematosus) cell test is positive in only about half of patients with SLE and is not used often now.
Blood Count. White and red blood cell and platelet counts are usually lower than normal and depending on severity are used to determine complications, such as anemia or infection.
If a skin rash is present, the physician may take a biopsy (a tissue sample) from the margin of a skin lesion. A test known as a lupus band detects antibodies known as immunoglobulin G (IgG), which are located just below the outer layer of the tissue sample. They are present in about 80% of patients with active SLE and in between 30% and 40% of those with inactive disease. The biopsy will not differentiate between systemic and discoid lupus, but it can rule out other diseases. Tests for other antibodies will rule out or confirm discoid lupus and subacute cutaneous lupus.
Tests for Serious Complications of SLE
Kidney Damage and Lupus Nephritis. Kidney damage in patients already diagnosed with SLE may be detected from the following tests:
Lung and Heart Involvement. A chest x-ray may be performed to check lung and heart function. An electrocardiogram and an echocardiogram are administered if heart disease is suspected.
Central Nervous System Complications. SLE occurring in the central nervous system (CNS) can be difficult to diagnose because its symptoms are easily confused with other psychiatric and neurologic conditions.
Osteoporosis. To detect early osteoporosis in SLE patients whose disease has lasted more than 3.5 years, experts recommend an imaging test called dual energy x-ray absorptiometry (DEXA) to measure bone mineral density.