F2 and cystic fibrosis: The available data regarding vitamin K status in CF patients are mainly based on the assessment of undercarboxylated prothrombin (PIVKA-II—protein induced by vitamin K absence), undercarboxylated osteocalcin (u-OC), or vitamin K1 (phylloquinone) levels [9,10,11,12,13,14,15,16,17,18].