Vitamin K (Phylloquinone)
Vitamin K is the group of substances essential for the formation of prothrombin and at least five other coagulation proteins, including factors VII, IX, and X and proteins C and S. The quinone-containing compounds are a generic description for menadione and derivatives exhibiting this activity. Vitamin K helps convert precursor forms of these coagulation proteins to functional forms; this transformation occurs in the liver. Dietary vitamin K is absorbed primarily in the terminal ileum and, possibly, the colon. Vitamin K is synthesized by intestinal bacteria; this synthesis provides 50% of the vitamin K requirement. Major dietary sources are cabbage, cauliflower, spinach and other leafy vegetables, pork, liver, soybeans, and vegetable oils. Uncomplicated dietary vitamin K deficiency is considered rare in healthy children and adults.
Vitamin K deficiency may be caused by antibiotic therapy, which results from decreased synthesis of the vitamin by intestinal bacteria. When vitamin K antagonists, such as warfarin sodium (Coumadin), are used for anticoagulant therapy, anticoagulant factors II, VII, IX, and X are synthesized but nonfunctional. An apparent vitamin K deficiency may lead to a hemorrhagic episode or may result when anticoagulants, such as warfarin sodium, are used.
Prothrombin time (velocity of clotting after addition of thromboplastin and calcium to citrated plasma) determination is an excellent index of prothrombin adequacy. Prothombin time is prolonged in vitamin K deficiency and in liver diseases characterized by decreased synthesis of prothrombin. Vitamin K deficiency also results in prolongation of the partial thromboplastin time, but the thrombin time is within the reference interval.
Toxicity from vitamin K is not commonly seen in adults. Large doses in infants may result in hyperbilirubinemia. The adult AI for vitamin K is 120 g/day for males and 90 g/day for females. In most laboratories, vitamin K is not assayed; however, prothrombin time is used as a functional indicator of vitamin K status. The normal prothrombin time is 11–15 seconds, which varies with method. With a vitamin K deficiency, the prothrombin time is prolonged. Several herbal supplements (e.g., garlic, gingko, and ginseng) may enhance the effects of Coumadin or interact with platelets, increasing the risk of bleeding.
Lab units Conversion Calculator. Convert Vitamin K (Phylloquinone) level to nmol/L, µg/L, µg/dL, µg/100mL, µg%, ng/mL
. Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Vitamin K (Phylloquinone).