Systemic Lupus Erythematosus - Diagnosis

(Page 3)

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 - 70% of patients who test positive for these antibodies.

Antiphospholipid Antibodies. In patients with SLE in whom blood abnormalities are suspected, tests will be administered to detect the presence of the two major antiphospholipid antibodies:

• The test for the lupus anticoagulant antibody measures the time it takes blood to clot. A longer than normal blood clotting time indicates a higher chance for clotting in the body and, therefore, the presence of lupus anticoagulant.
• An ELISA test (enzyme-linked immunosorbent assay) is performed to detect the anticardiolipin antibody.

---

---

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 patients with SLE 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 no longer used that often.

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.