A recent study found that it is possible to distinguish patients with systemic lupus erythematosus (SLE) from those with primary fibromyalgia (FM), with complete specificity, using a new test that measures the levels of abundant proteins in circulation. The study, “Systemic lupus erythematosus and primary fibromyalgia can be distinguished by the test of products of complement activation linked to the cell”, was published in Lupus Science & Medicine.
SLE is a systemic autoimmune disease in which patients experience a variety of symptoms including chronic pain, arthralgia, fatigue and morning stiffness. Many, however, present symptoms that are not specific and do not agree with the formal criteria established by the American College of Rheumatology. As a result, they can remain undiagnosed for a long time.
SLE has been distinguished from other diseases by combining the clinical history, demographic information and age of onset of the disease with a clinical examination accompanied by laboratory tests for antinuclear antibodies (ANA), among other autoantibodies specific to SLE. However, the specificity of this test for SLE is questioned, given that about 14 percent of the general population is also positive for antinuclear antibodies, as it is, importantly, 15 to 25 percent of people with FM.
The researchers investigated whether a test had already been shown to be more sensitive compared to anti-DNA antibodies (the standard method for diagnosing SLE) and was an effective strategy for differentiating SLE from primary FM. The test combines biomarkers of cell-bound complement activation products (CB-CAP) (including erythrocytes-C4d, EC4d and B-C4d lymphocytes, BC4d) with standard autoantibodies of rheumatic disease in a multiple analysis assay with algorithm (MAAA ).
A total of 75 adult individuals with SLE and 75 adults with primary FM with a confirmed diagnosis were studied (using appropriate classification criteria). The researchers measured both CB-CAP and antinuclear antibodies followed by CB-CAP and MAAA. The team found that CB-CAPs in MAAA could be evaluated in 138 of the 150 enrolled subjects (92 percent) and resulted in 60 percent sensitivity for SLE, while reporting negative results for each FM patient tested , for which they gave a specificity of 100 percent.
“We believe that this practical tool with improved performance compared to the traditional complement measure (C3 / C4) can help establish a diagnosis of SLE. In addition, it is a practical measure of complement activation, since the blood sample can be sent during the night from the doctor’s office to the laboratory, “the authors wrote.
These results suggested that the CB-CAP in the MAAA test are able to differentiate the SLE from the FM, with a particular meaning for the patients positive for antinuclear antibodies. “The measurement of CB-CAP in MAAA could facilitate the appropriate referral of symptomatic patients with positive ANA to the rheumatologist, and thus help initiate the appropriate course of treatment,” the authors concluded.