Evaluation of the Mucin Glycoprotein (KL‑6) as a Prognostic Factor in COVID‑19 Patients

Lung damage caused by SARS-CoV-2 infection has been described in the literature as resulting from direct cytopathic effects on type II pneumocytes, playing a critical role in the extent and progression of pulmonary injury. This study aimed to evaluate the prognostic value of the mucin glycoprotein KL-6 in predicting clinical outcomes in COVID-19 patients. We prospectively enrolled 260 COVID-19 patients admitted to specialized hospitals in Naples under the ASL Napoli 1 Centro between March 20, 2020, and March 31, 2022, when the state of emergency ended. Our institution, part of the Coronet Lab network designated by the Campania Region and the Ministry of Health, performed 203,368 molecular tests for COVID-19 during this period, identifying 17,650 positive cases (8.67%). The study cohort had a median age (IQR) of 63 years (54–72), comprising 199 males and 61 females. All patients underwent clinical, radiological, and functional assessments in the emergency department. Serum KL-6 levels were measured at admission, after detecting interstitial lung damage, and during hospitalization. Elevated KL-6 concentrations were observed in patients with pulmonary abnormalities, and baseline levels demonstrated good accuracy in identifying those with radiologically documented fibrotic sequelae. In hospitalized COVID-19 patients, serum KL-6 levels also correlated with severe cases requiring mechanical ventilation and predicted the development of fibrotic lung sequelae during follow-up. Finally, KL-6 proved to be an effective predictive marker of disease severity, emphasizing its potential role in guiding clinical management and prognosis.