In the present study, we evaluated the time-varying diagnostic performance of biomarkers measured at admission only and updated the biomarkers at several time points in routine clinical settings. The performance of the updated biomarkers by the ID approach was higher than that of the baseline biomarkers in all situations, with the exception of the 1st week (0.713 vs. 0.653) for WBC (Tables 1 and 2). The performance of the updated biomarkers by the CD approach was higher than that of the baseline biomarker in most parameters, except for lactate in the 1st week (0.756 vs. 0.699), WBC in the 1st (0.689 vs. 0.572) and 2nd (0.679 vs. 0.615) week, TB in the 1st (0.617 vs. 0.595) and 6th (0.483 vs. 0.438) week, and creatinine in the 6th week (0.540 vs. 0.288) (Tables 4 and 5). From the results, we identified that patient biomarkers must be regularly updated to maintain prognostic accuracy because good prognostic markers effectively suggest the choice and timing of therapeutic interventions, allowing timely action for individuals with the greatest risk of complications.
The updated platelet biomarker had the highest c-index of 0.930 (95% CI, 0.919–0.941), which keeps the AUC ID over 0.930 over time, indicating that it is a strong prognostic biomarker for practical use. Moreover, we used AUC CD over a period of 1 week to actually evaluate the use of updated biomarkers as a decision tool. We found that the AUC CD of platelet was consistently higher than 0.870 across all selected time points except at weeks 4 and 6. This indicates that platelet identifies high-risk patients at a high-risk of mortality. Cate et al. (12) reported that platelet count is a strong predictor of mortality and reported an AUC of 0.779 (95% CI 0.697–0.862), which was calculated by the value measured on the third day after admission. Huang et al. (13) reported that platelets could be a biomarker of mortality, with an AUC value of 0.782. Lactate has been used as a predictor of cellular hypoxia and shock, with an AUC value of 0.82, indicating high prognostic performance (14). Adding lactate to the severity scores predicts mortality better in critically ill patients. (15) In our study, lactate showed a relatively lower c-index (0.786) than platelets, PT, and creatinine. This could be because lactate further reflects the severity of burn than that of mortality. Creatinine is also a better risk factor of AKI rather than that of mortality (16). However, creatinine showed high discrimination, with a c-index of 0.828. This is probably because AKI is one of the most common complications in burn patients. PT showed a high c-index of 0.862 because PT was reported as a predictor in many diseases, such as liver disease, cardiac disease, and trauma (17–19). PT is reported to be an early predictor of hepatic dysfunctions (20). However, it was a good predictor throughout the period.
This study has some limitations. First, it was not multicenter study; thus, our population does not represent the entire population of Korea. However, our center is the only unit run by the University of Korea. Second, we set an arbitrary window period of 1 week for the CD approach to compare the biomarkers; thus, we cannot conclude how often the biomarkers should be updated.