Vitamin K and Cystic Fibrosis

Vitamin K is a fat-soluble vitamin required in the carboxylation and subsequent activation of clotting factors and bone proteins, including osteocalcin and glutamic acid protein. Those patients deficient in vitamin K are at risk for clotting disorders and decreased bone mineral density. Patients with cystic fibrosis (CF) are at risk of vitamin K deficiency because of an inability to absorb fat because of pancreatic insufficiency. Other possible causes of vitamin K deficiency in CF include liver disease, chronic antibiotic use, and possible bowel resection of those patients with a history of meconium ileus. The most sensitive diagnostic test for vitamin K deficiency is undercarboxylated osteocalcin. Plasma prothrombin in vitamin K absence II is also a sensitive marker of vitamin K deficiency. The measurement of prothrombin time is a less sensitive marker of vitamin K status because it is not elevated until more than 50% of vitamin K stores are depleted. Supplementation with 0.3–0.5 mg/day of vitamin K is recommended for patients with CF, although larger doses may be more effective in preventing insufficiency.