Background: Interleukin-6 (IL-6) rises rapidly during systemic inflammation and is used in some ICUs as a daily infection marker. Whether routine IL-6 monitoring affects patient outcomes or antimicrobial use, compared with standard biomarkers CRP/PCT, remains unclear. Methods: This retrospective two-step study was conducted at a tertiary interdisciplinary ICU in Wiesbaden, Germany. Step 1 (pilot cohort) compared two 2-month periods with routine IL-6 versus CRP/PCT testing to identify differences and generate assumptions. Step 2 (extended cohort) compared two consecutive 12-month periods before and after discontinuation of IL-6 testing. After matching for disease severity and specialty, endpoints included ICU length of stay, ventilation hours, mortality, and antimicrobial use measured as defined daily doses (DDD), and recommended daily doses (RDD) per 100 patient-days. Results: Results: In the pilot cohort (n = 221), there were no significant differences between the IL-6 and CRP/PCT groups in terms of anti-infective therapy or ventilation hours. In the extended cohort (n = 5146), case-matched analyses showed no significant group differences in ICU length of stay, ventilation hours, or mortality between groups. Antimicrobial consumption was higher when IL-6 was used: DDD (16.8% increase, rate ratio RR = 1.17, 95% CI (1.14, 1.19), p < 0.001) and RDD (11.6% increase, RR = 1.12, 95% CI (1.09, 1.14), p < 0.001). Conclusions: In this exploratory study, routine IL-6 testing was not associated with improved outcomes but might be linked to increased antimicrobial consumption.
Bexten et al. (Wed,) studied this question.