Application of procalcitonin, white blood cell count and neutrophil-to-lymphocyte ratio in the diagnosis of systemic lupus erythematosus with a bacterial infection

Background: Systemic lupus erythematosus (SLE) is an autoimmune disease. This study aims to analyze the value of procalcitonin (PCT), white blood cell count (WBC), and neutrophil-to-lymphocyte ratio (NLR) in the differential diagnosis of SLE with a bacterial infection. Methods: A total of 164 patients with SLE admitted to our hospital from January 2018 to December 2019 were selected as the research subjects. According to the results of bacterial culture, patients with SLE were divided into the bacterial infection group (46 cases) and the non-bacterial infection group (118 cases). Sixty healthy volunteers without the allergic disease, family history of tumors, or immunodeficiency in the same age group were selected as the control group during the same period. Fasting venous blood was collected in the morning to detect serum macrophage migration inhibitory factor (MIF), C-reactive protein (CRP), red blood cell distribution width (RDW), PCT, WBC, neutrophil count ( NEUT) and lymphocyte count (LYMPH), and the NLR (NEUT/LYMPH) was calculated. Results: CRP, PCT, WBC, and NLR levels were significantly higher in the bacterial infection group and the non-bacterial infection group than that in the control group, and which in the bacterial infection group is significantly higher than in the non-bacterial infection group (P<0.05). PCT, WBC and NLR were independent risk factors for SLE with bacterial infection (P<0.05). ROC curve analysis showed the areas under the curve of PCT, WBC, and NLR for the differential diagnosis of SLE with bacterial infection being 0.883, 0.669, and 0.624. Then, the sensitivities of 78.3%, 43.5%, and 69.6% were observed with the specificities of 98.3%, 91.5%, and 56.8%, respectively. The area under the curve of combined prediction was 0.919, with a sensitivity of 78.3%, and a specificity of 97.5%. These results showed that the value of the combined prediction was significantly higher than the single prediction of each indicator. And the levels of PCT, WBC, and NLR gradually decreased with the progress of treatment (P<0.05). Conclusions: The combined detection of PCT, WBC, and NLR levels shows high sensitivity and specificity for SLE with a bacterial infection, which can be used for early auxiliary diagnosis of SLE with a bacterial infection.