Therefore, this study aimed to develop and validate a novel LC–MS/MS method characterized by a broad calibration curve range to comprehensively and sensitively determine KKS peptides (bradykinin, kallidin, des-Arg(9)-bradykinin, des-Arg(10)-kallidin, bradykinin 1-7, bradykinin 1-5 and bradykinin 2-9) to enable reliable insights into their alterations in COVID-19—or other disease states (e.g. allergies or lung cancer)—in comparison to controls. Here, KNG1 is linked to lung cancer.