Circulating calprotectin levels are associated with lung damage and disease outcome in patients with COVID-19

Objective The present study aimed to investigate whether circulating calprotectin levels were associated with the extent of lung parenchyma involvement, laboratory parameters of inflammation/organ damage, and clinical outcome in patients with SARS-CoV-2 infection.Methods A retrospective observational cohort study was conducted enrolling 172 adult patients with laboratory-confirmed SARS-CoV-2 infection. The extent of lung parenchyma involvement was assessed using a validated high-resolution computerized tomography (HRCT)-based stratification system. Serum calprotectin concentrations were quantified using the QUANTA Flash Circulating Calprotectin Reagents. Routine laboratory parameters were collected from clinical records. In a subset of patients who received tocilizumab (n = 56), serum samples were longitudinally collected.Results Circulating serum calprotectin levels were significantly associated with the extent of CT-assessed pulmonary involvement, markers of systemic inflammation, and adverse clinical outcomes (mechanical ventilation requirement and in-hospital death). A calprotectin threshold of 3.86 μg/mL showed high sensitivity for identifying patients with ≥40% lung parenchyma involvement, while a threshold of 13.73 μg/mL showed high specificity for adverse clinical outcomes. Longitudinal monitoring of calprotectin in tocilizumab-treated patients revealed that rising levels during follow-up were associated with death or tracheotomy, independent of baseline values.Conclusion Our findings support the clinical utility of circulating calprotectin as a complementary biomarker in COVID-19 management.