Diagnostic Value of Procalcitonin and Interleukin-6 on Early Postoperative Pneumonia after Adult Cardiac Surgery: A Prospective Observational Study.

BACKGROUND Postoperative pneumonia (PP) is the most common primary infection after cardiac surgery, increasing the hospitalization expense and causing the consumption of healthcare resources. This study aimed to investigate the diagnostic value of procalcitonin (PCT) and interleukin-6 (IL-6) on early postoperative pneumonia after adult cardiac surgery. METHODS In this prospective observational study, patients with pneumonia and age- and sex-matched cases in our center from October 10, 2020 to January 31, 2021 were included. Patients diagnosed with pneumonia in this study needed meet both clinical and microbiological diagnostic criteria. Blood samples were collected in all patients from postoperative day (POD) 1 to postoperative day 5 to detect PCT, IL-6, white blood cell count, and C-reactive protein. The diagnostic performance of different biomarkers was evaluated by the receiver operating characteristic curves and the area under the curves. RESULTS Our study enrolled 272 patients, including 24 patients with postoperative pneumonia and 248 age- and sex-matched cases. From POD1 to POD5, the absolute value of PCT and PCT variations showed diagnostic significance for pneumonia (P < .05); the diagnostic value of the absolute value of IL-6 and IL-6 variations was not satisfying. White blood cell count showed no differences; C-reactive protein had no diagnostic value before POD4. Multivariable logistic regression showed that PCT variation and IL-6 variation from POD3 to POD1 were the strongest risk factors for postoperative pneumonia [OR:12.50, 95% CI: (3.40-45.5); OR:13.71, 95% CI: (1.11-168.47)]. According to the above results, we defined the PL Index. PL Index showed the best diagnostic value among those biomarkers in POD3 [AUC: 0.90, 95% CI: (0.79-0.95)]. Multivariable logistic regression showed PL Index POD3 has significant correlation with postoperative pneumonia [OR:1.23, 95% CI: (1.11-1.37), P = .041]. CONCLUSIONS PCT variation and IL-6 were more accurate than C-reactive protein and white blood cell count to predict early postoperative pneumonia, but the diagnostic properties of PCT could not be observed during the first three postoperative days due to the inflammatory process. By combining the variations of PCT and IL-6, we defined the PL Index, which shows the best diagnostic ability on early postoperative pneumonia after adult cardiac surgery.