Diagnostic Value of Serum Procalcitonin and Erythrocyte-bound Complement Component 4d (E-C4d) Levels in Differentiating a Flare-up from a Bacterial Infection in Egyptian Patients with Systemic Lupus Erythematosus

Background The distinction between bacterial infection and febrile flare in patients with systemic lupus erythematosus (SLE) has always been a crucial yet difficult step in the management of these patients. Although the presentation looks similar, the treatment is extremely different and increases the burden on health care systems, particularly in low-income countries. Aim of this study This study aimed to investigate the potential value of combining serum procalcitonin (PCT) and erythrocyte-bound Complement Component 4d (E-C4d) measurements in distinguishing infection from disease flare in patients with SLE. Methods Serum levels of these two biomarkers were analyzed in patients with positive aerobic bacterial cultures, patients with flare-up fever showing no signs of infection, and a control group with medical diseases other than SLE. Results The PCT level was found to be high in patients with bacterial infections and is considered a suitable marker to exclude cases of SLE with bacterial infections. Additionally, E-C4d was found to have a positive correlation with SLE flare-ups. Conclusion Our findings suggest that the use of serum PCT and E-C4d simultaneously may help differentiate between lupus flares and bacterial infection. However, this observation needs further validation in larger studies.