A recent study found it is possible to distinguish systemic lupus erythematosus (SLE) patients from those with primary fibromyalgia (FM), with complete specificity, using a new test measuring the levels of abundant proteins in circulation. The study, “Systemic lupus erythematosus and primary fibromyalgia can be distinguished by testing for cell-bound complement activation products,” was published in Lupus Science & Medicine.

SLE is an autoimmune systemic disease with patients experiencing a variety of symptoms that include chronic pain, arthralgia, fatigue, and morning stiffness. Many, however, present symptoms that are non-specific and not in agreement with the formal criteria established by the American College of Rheumatology. As a result, they may long remain undiagnosed.

SLE has been distinguished from other diseases by combining clinical history, demographic information, and age at disease onset with a clinician examination accompanied by laboratory tests looking for antinuclear antibodies (ANA), among other SLE-specific autoantibodies. However, the specificity of this test for SLE is challenged, given that around 14 percent of the general population is also positive for antinuclear antibodies as are, importantly, 15 percent to 25 percent of people with FM.

Researchers investigated if a test had already proved more sensitive when compared with anti-DNA antibodies (the standard method for SLE diagnosis), and was an effective strategy for differentiating SLE from primary FM. The test combines cell-bound complement activation products (CB-CAPs) biomarkers (including erythrocyte-C4d, EC4d and B-lymphocyte-C4d, BC4d) with standard rheumatic disease autoantibodies into a multi-analysis assay with algorithm (MAAA).

A total of 75 SLE and 75 primary FM adult individuals with confirmed diagnosis (using appropriate classification criteria) were studied. Researchers measured both CB-CAPs and antinuclear antibodies followed by CB-CAPs-MAAA. The team found that CB-CAPs in MAAA could be evaluated in 138 of the 150 subjects enrolled (92 percent) and resulted in 60 percent of sensitivity for SLE, while reporting negative results for every FM patient tested, therefore rendering a 100 percent specificity.

“We believe that this practical tool with enhanced performances compared with traditional complement measure (C3/C4) can help establish a diagnosis for SLE. Moreover it is a practical measure of complement activation as blood specimen can be shipped overnight from the physician office to the laboratory,” the authors wrote.

These results suggested that the CB-CAPs in MAAA test is capable of differentiating SLE from FM, with a particular significance for patients positive for antinuclear antibodies. “The measurement of CB-CAPs in MAAA could facilitate the appropriate referral of symptomatic patients with a positive ANA to the rheumatologist, and thus help initiate appropriate course of treatment,” the authors concluded.