Vitamin K

• Sources
  • Leafy green vegetables (vitamin K1)
  • Eggs, dairy, and meat (vitamin K2)
  • Synthesized in small amounts by intestinal bacteria
    • Use of antibiotics can increase the effect of warfarin. See Warfarin interactions

Vitamin K deficiency

• Etiology
  • Newborns: Sterile gut (no bacterial synthesis), poor placental transfer, and low content in breast milk. This is why all newborns receive prophylactic IM vitamin K at birth to prevent hemorrhagic disease of the newborn.
  • Malabsorption: Celiac disease, Crohn’s disease, cystic fibrosis, biliary obstruction (fat-soluble vitamin).
  • Broad-spectrum antibiotics: Suppress normal gut flora that synthesize vitamin K.
  • Liver failure: Decreased production of clotting factors and inability to store vitamin K.
  • Warfarin therapy: Iatrogenic cause.
• Clinical Features
  • Bleeding diathesis.
  • Easy bruising, mucosal bleeding (epistaxis, gingival bleeding), hematuria, GI bleeding (melena), intracranial hemorrhage (newborns).
  • Petechiae and purpura are typically absent as platelet function is normal.
• Diagnostics
  • ↑ PT/INR: Factor VII has the shortest half-life, so the extrinsic pathway (measured by PT) is affected first and most severely. This is the most sensitive initial finding.
  • ↑ PTT: In severe or prolonged deficiency, factors II, IX, and X are depleted, prolonging the intrinsic pathway (measured by PTT).
  • Normal bleeding time: Platelet count and function are unaffected.
  • Normal fibrinogen & D-dimer.
  • Dx is confirmed by normalization of PT after vitamin K administration.
• Treatment
  • Vitamin K supplementation (phytonadione). Can be given PO, IV, or IM.
  • For life-threatening bleeding associated with warfarin, give Fresh Frozen Plasma (FFP) or prothrombin complex concentrate (PCC) for rapid reversal, along with IV vitamin K.