ABSTRACT
Background: Recent reports identified enrichment of T cells and monocytes in the BAL fluid of patients with COVID-19 pneumonia, in contrast to neutrophilia in patients with non-COVID-19 pneumonia, which suggests a distinct immunopathology. We evaluated whether AKI, an independent risk factor for adverse outcomes, modifies BAL cell composition in critically ill patients. Methods: We retrospectively analyzed BAL specimens from 710 critically ill patients undergoing evaluation for pneumonia at an academic medical center from 3/2018-11/2020. Kruskal-Wallis tests compared distributions of BAL fluid % cell counts by COVID-19 and AKI status. Multivariable linear regression models tested the associations of COVID-19 status with the BAL fluid % cell counts. We tested for effect modification by AKI status. AKI was defined by the KDIGO criteria. Results: Mean age was 60±15 years and median baseline serum creatinine was 0.8 [0.6-1.1] mg/dl. COVID-19 was positive in 34.5% and AKI occurred in 42.8% of patients. Figure 1A shows differences in BAL fluid cell composition by COVID-19 and AKI status. Highest % of neutrophils were in COVID-19(-) AKI(-) patients and lowest in COVID-19(+) AKI(-) patients. Macrophages, monocytes, and lymphocytes were highest in COVID-19(+) AKI(-) patients and lowest in COVID-19(-) AKI(-) patients. COVID-19(+) patients had a significantly lower % of neutrophils and a higher % of monocytes and lymphocytes after multivariable adjustment (Figure 1B). Patients who were AKI(+) had decreased % of neutrophils when COVID-19(-), while the opposite effect was noted for COVID-19(+) (P for interaction=0.007). Conclusions: AKI may differentially modify the cell BAL fluid cell composition among patients with suspected pneumonia based on their COVID-19 status.