A 3-year-old girl with cystic fibrosis has easy bruisability. Which vitamin deficiency is most likely?

The scenario describes a young girl with cystic fibrosis who is experiencing easy bruisability, which is a key symptom often linked to deficiencies in certain vitamins involved in blood clotting. In the case of cystic fibrosis, it is common for patients to have issues with fat absorption due to pancreatic insufficiency. This can lead to deficiencies in fat-soluble vitamins, including vitamins A, D, E, and K.

Vitamin K is essential for the synthesis of clotting factors II (prothrombin), VII, IX, and X in the liver. A deficiency in vitamin K can lead to bleeding disorders and easy bruising, as the body lacks the necessary components to properly form blood clots. In a patient with cystic fibrosis, who may not be absorbing nutrients effectively due to pancreatic enzyme insufficiency, a vitamin K deficiency is particularly plausible.

Other vitamins or factors mentioned have different implications. For instance, vitamin B12 is primarily associated with anemia and neurological issues, while vitamin C deficiency is tied to scurvy and may lead to bruising through different mechanisms, such as affecting collagen synthesis. Antithrombin III is a protein that helps regulate blood clotting but is not a vitamin and its deficiency typically results in thrombosis rather than easy bruis