The role of procalcitonin, neutrophil–lymphocytic ratio, and monocytic count in differentiation between systemic lupus activity and bacterial infection in patients with systemic lupus erythematosus

Background The complicated autoimmune disease known as systemic lupus erythematosus (SLE) is typified by a variety of clinical symptoms, the development of pathogenic autoantibodies, the deposition of immune complexes, and end-organ destruction. Aim This study aimed to evaluate the procalcitonin (PCT), neutrophil–lymphocyte ratio (NLR), and monocyte count’s diagnostic usefulness in distinguishing between SLE flares and secondary bacterial infections in lupus patients. Patients and methods This cross-sectional comparative study involved 90 patients, aged 18–55 years, classified into three equal groups: group I (SLE patients with lupus flare, MEX-SLEDAI >5), group II (SLE patients with secondary bacterial infection), and group III (healthy controls). Diagnostic performance of PCT, NLR, and monocyte count were evaluated. Results In comparison to SLE patients experiencing lupus flare-ups, individuals with bacterial infections had considerably higher levels of PCT, NLR, and monocytes. With a sensitivity of 93.3%, specificity of 73.3%, and area under the curve of 0.813, the PCT cut-off value of less than or equal to 0.011 was obtained. For NLR and monocytes, the cut-off values were less than or equal to 2.20 and less than or equal to 407.5, with the respective areas under the curves of 0.668 and 0.671, sensitivities of 86.7 and 90.0%, and specificities of 73.3 and 70.0%. Conclusion PCT, NLR, and monocytes serve as important biomarkers for distinguishing bacterial infections from lupus flares in SLE patients. Among these, PCT demonstrated superior diagnostic performance, making it a reliable tool for early differentiation between bacterial infections and SLE flares.