A new haematological model for the diagnosis and prognosis of severe community-acquired pneumonia: a single-center retrospective study.

Background: Severe community-acquired pneumonia (sCAP) is a condition where infection-induced lung tissue inflammation intensifies to a certain stage, resulting in organ dysfunction and even life-threatening disease. When sCAP occurs, neutrophils and monocytes will be activated and released into the peripheral blood to kill bacteria. There are significant morphological changes in these activated neutrophils and monocytes. Haematological parameters can reflect these morphological changes, and indicate the occurrence of sCAP and the severity of infection. This study is designed to establish a new haematological model and explore its clinical value in the diagnosis and prognosis of sCAP. Methods: Patients who fulfilled the diagnostic criteria of common pneumonia (CP) and sCAP were enrolled in this study. Healthy body check-up patients were also enrolled as a control group. Characteristic information and 28-day survival of patients were recorded. Haematological results, C-reactive protein (CRP) and procalcitonin (PCT) were calculated by BC-6800 Plus automated haematology analyser and cobas E601 automated biochemical immunoassay analyser. Results: A total of 100 check-ups patients, 100 CP patients, and 111 sCAP patients were enrolled in this study. The new haematological model WBC & Mon-XW, combining WBC (white blood cell count) and Mon-XW (monocytes complexity distribution width), was significantly elevated in the sCAP group and significantly higher than in the control group and the CP group. The new model had good diagnostic efficacy for sCAP, with an area under the receiver operating characteristic curve (ROC-AUC) of 0.842, which was higher than that of CRP (0.633) and PCT (0.750). Moreover, WBC & Mon-XW was effective for survival prognostic evaluations of sCAP, with an ROC-AUC of 0.748. The new model was the independent predictors for the death of pneumonia with an OR (odds ratio) value of 1.82. The 28-day mortality rate was approximately 40% in the WBC & Mon-XW ≥8.9 group, which was approximately 15% higher than that in the WBC & Mon-XW <8.9 group. Conclusions: The new haematological model can be used as an indicator for sCAP diagnosis and prognosis.