Fat-Soluble Vitamins — A, D, E, K

Vitamin K is essential for the synthesis of which of the following clotting factors through γ-carboxylation?

A 58-year-old man with a 20-year history of alcohol use disorder presents with progressive vision loss, night blindness, and bitot spots on conjunctival examination. His dietary intake is poor, consisting mainly of refined carbohydrates and alcohol. Serum retinol level is 15 µg/dL (normal: 30–100 µg/dL). Which of the following best explains the pathophysiology of his night blindness?

A 62-year-old man with chronic liver disease (Child-Pugh B) and steatorrhea presents with easy bruising, epistaxis, and an INR of 3.2 (normal <1.2). Prothrombin time is prolonged. Serum albumin is 2.8 g/dL. What is the most appropriate next step in management?

A 72-year-old woman on long-term warfarin therapy for atrial fibrillation presents with spontaneous bruising, epistaxis, and a prolonged prothrombin time (PT 18 seconds, INR 4.2). She has been taking high-dose vitamin E supplements (1200 IU daily) for the past 6 months on the advice of a friend. Her dietary intake of leafy green vegetables has remained unchanged. Which of the following best explains the mechanism of her coagulopathy?

Which of the following is the active form of vitamin A that functions as a cofactor in the visual cycle?