Used to measure pepsin levels in saliva or lung secretions as a biomarker for gastroesophageal reflux disease (GERD) and aspiration in patients with respiratory symptoms. Enables early detection and monitoring of reflux-related conditions, especially in chronic cough, asthma, and idiopathic pulmonary fibrosis. Provides a non-invasive, sensitive, and specific method for diagnosing extraesophageal reflux. Widely used in clinical research and diagnostic laboratories to assess reflux severity and treatment response.