Severe COVID‐19 represents viral pneumonia from severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection leading to ARDS. The prognosis of patients with the severe condition is poor; thus, biomarkers for earlier prediction of COVID-19 progression are vital. Recently, we identified stratifin (SFN) as a serum biomarker for diffuse alveolar damage, a major pathological condition of ARDS. In this study, we compared and evaluated the predictive performances of five lung injury-related biomarkers: lung surfactant protein-D (SP-D), the sialylated carbohydrate antigen KL-6, the sepsis marker presepsin (P-SEP), and kallistatin and SFN.
We measured concentrations of these proteins in serum samples collected serially during hospitalization from patients recovering from mild disease (mild and moderate cases) or patients who developed to severe COVID-19 pneumonia (severe and critical cases requiring oxygen administration and invasive ventilation). This analysis showed that SFN as well as P-SEP were elevated with the onset of severe or critical symptoms in COVID-19 patients and decreased with symptom improvement. Changes in serum levels of SFN was distinctly earlier than those in SP-D and KL-6, also known as biomarkers for pulmonary fibrosis, and even peripheral oxygen saturation (SpO₂) values, with significantly higher values several days before patient onset severe disease. SFN, as well as P-SEP, may be useful prognostic biomarkers for COVID-19 severity.