Aims 85% of children with cystic fibrosis (CF) have pancreatic insufficiency, leading to chronic malabsorption of fats and fat-soluble vitamins. Whilst vitamin A, D and E supplementation is commonplace, evidence is currently lacking to support routine vitamin K supplementation. This study aims to use new data, available since the introduction of serum vitamin K testing in one CF clinic, to further inform this debate.

Methods Serum vitamin A, D, E and K levels, liver function tests (LFTs) and coagulation assays, recorded annually for three years, were collected from the notes of 106 children with CF. The prevalence of vitamin K deficiency (defined as <0.25 nmol/mmol triglyceride) was calculated, and associations between this deficiency and other biochemistry abnormalities were investigated using a case-control format, comparing persistently deficient cases (deficient on ≥ 2 years) to controls who were always sufficient. LFT and coagulation derangement were defined as elevation of ALT/ALP/GGT/PT/APTT above age-specific laboratory reference ranges. Statistical analyses were performed using “MedCalc” software.

Results 52% of the total group had been vitamin K deficient at least once. This was the most common deficiency, followed by vitamin D (19%), and was not associated with other fat-soluble vitamin deficiencies. Of the 79 children with results available for ≥ 2 years, 18% were persistently deficient, 45% were deficient once only, and 37% were always sufficient. Coagulopathy was common (53%) but only weakly associated with vitamin K deficiency (odds ratio (OR)=1.2). LFT derangement was also common (23%); the strongest association being found between elevated GGT and vitamin K deficiency (OR=4.7). However these results were not statistically significant.

Conclusion Vitamin K deficiency was very common in this group of CF patients, but the expected strong association with coagulopathy was not seen. More research is therefore needed to clarify the clinical significance of this deficiency, perhaps through looking at other functions of vitamin K such as the maintenance of bone health. The association found with elevated GGT, which can be an early marker of CF liver disease, could also be investigated to see if this association is reproduced in a larger study.