Although we did not document differences in PIVKA-II levels between selected subgroups, it is worth mentioning that undercarboxylated prothrombin concentrations were higher in CF patients not receiving (n = 7) vitamin K than those receiving (n = 56) supplementation (3.37 <2.07–3.97> vs. 1.48 <0.74–2.90> ng/mL, p = 0.0821). Here, F2 is linked to cystic fibrosis.