Ramsey-Goldman R, Alexander RV, Massarotti EM, et al. - In this investigation, researchers assessed the frequency of cell-bound complement activation products (CB-CAPs) as a complement activation marker for patients suspected of systemic lupus erythematosus (probable SLE [pSLE]) and the usefulness of this biomarker as a predictor of the American College of Rheumatology (ACR) criteria's evolution of pSLE into classified SLE. Both ACR and Systemic Lupus International Collaborating Clinics criteria, primary Sjogren's syndrome and other rheumatic diseases enrolled patients suspected of SLE by lupus experts and meeting 3 ACR SLE (pSLE) classification criteria. More recently, the 92 pSLE were diagnosed than the 53 established SLE and the use of antirheumatic drugs was lower. For CB-CAPs or multianalyte assay panel (MAP), more pSLE was positive than low complement during the registration visit. Complement activation occurs in few patients with pSLE and CB-CAPs and MAP can detect greater frequencies than traditional serum complement protein levels. Positivity of MAP above 0.8 predicts a shift to classifiable SLE based on ACR criteria.