SF is synthesized by reticuloendothelial cells and hepatocytes, and has the function of tissue repair and immunosuppression.18 The serum SF level can reflect the degree of inflammation and lung injury, and is closely related to the occurrence and development of respiratory distress syndrome.19 PAI-1 and urokinase-type plasminogen activator (uPA) are important members of the fibrinolytic family. Here, PLAU is linked to newborn respiratory distress syndrome.