Critical evaluation of “Exploratory characterization of dynamic soluble programmed death-ligand 1 trajectories and their association with mortality in critical COVID-19”

Recent work describing longitudinal soluble programmed death-ligand 1 (sPD-L1) trajectories in critically ill patients with COVID-19 provides valuable insight into immune checkpoint dynamics and mortality risk. However, interpretation of these findings warrants caution. Longitudinal analyses are vulnerable to survivorship and informative censoring bias, potentially overstating declining biomarker trends among survivors. In addition, the absence of time-varying adjustment for evolving disease severity and organ support limits causal inference regarding sPD-L1 as an independent prognostic marker. Finally, renal dysfunction may confound circulating sPD-L1 concentrations through impaired clearance. Addressing these methodological issues is essential for validating sPD-L1 as a robust prognostic biomarker in critical illness.