Evaluation of the significance of interleukin-6 in the diagnosis of postoperative pneumonia: a prospective study

Background Postoperative pneumonia (PP) is one of the most common complications after cardiac surgery. This study was designed to access the diagnostic value of interleukin-6 (IL-6) for pneumonia within the first 5 days after cardiac surgery in adults. Method This prospective observational study enrolled 694 patients who admitted to our center from 10 October 2020 to 30 June 2021. Blood samples were collected after admission and on five consecutive days after surgery to measure IL-6, procalcitonin (PCT), C-reactive protein (CRP) and white blood cells (WBC) respectively. Combined with clinical data, we assessed the diagnostic performance of different biomarkers using univariate and multifactorial analyses as well as receiver operating characteristic curves (ROC) and the area under the curve (AUC). Result Finally, 68 patients were diagnosed with PP (PP Group). In addition, 626 cases were assigned to the control group (Non-PP Group). From postoperative day 1 (POD1) to day 5, IL-6 and PCT levels showed higher diagnostic value (P < 0.001, P < 0.05, respectively); meanwhile, there was no difference in white blood cell counts between the two groups; CRP showed some value from POD2 onwards (P < 0.001). Among these biomarkers, IL-6 on POD1 [AUC: 0.78, 95% confidence interval (CI): 0.71–0.83], IL-6 on POD2 (AUC: 0.77, 95% CI: 0.71–0.82) and CRP levels on POD3 (AUC: 0.77, 95% CI: 0.70–0.84) had the highest diagnostic value. Multivariate analysis found that smoking status [odds ratio(OR): 7.79, 95% CI: 3.05, 19.88, p < 0.001], drinking status (OR: 22.68, 95% CI: 9.29, 55.37, p < 0.001) and hypertension (OR: 2.85, 95% CI: 1.28, 6.35, p = 0.011), IL-6 on POD2 (OR: 1.01, 95% CI: 1.00, 1.01, p = 0.018), mechanical ventilation time (OR: 1.03, 95% CI: 1.00, 1.05, p = 0.040) and intensive care unit stay time (OR: 1.01, 95% CI: 1.00, 1.02, p < 0.001) were independent risk factors for postoperative pneumonia. Conclusion Smoking, drinking, hypertension, prolonged duration of mechanical ventilation and intensive care unit stay, and IL-6 on POD2 were independent risk factors for pneumonia after cardiovascular surgery. IL-6 level on POD2 may serve as a promising indicator, better than WBC, PCT and CRP.