Vitamin K Deficiency

Summary

Vitamin K deficiency typically presents with bleeding or hemorrhage. Causes include insufficient intake (malnourishment) or insufficient production by gut flora. Specifically, Crohn's disease, cystic fibrosis, and other causes of pancreatic insufficiency can lead to poor absorption of this fat-soluble vitamin. Insufficient production by gut flora is of particular concern in newborns, as their sterile intestines are unable to synthesize vitamin K. This leads to a condition known as hemorrhagic disease of the newborn, which is characterized by increased PT (and PTT) but normal bleeding time. Likewise, prolonged antibiotic use (broad-spectrum) may disturb gut flora, which again may lead to impaired synthesis of vitamin K and subsequent deficiency.

Key Points

• Vitamin K Deficiency
  • Typically seen with fat malabsorption (e.g. cystic fibrosis, pancreatic insufficiency, Crohn’s), malnourishment, or long-term antibiotic use
    • fat-soluble vitamin synthesized by intestinal bacteria
• Hemorrhage due to decreased Vitamin K-dependent clotting factors
  • Neonatal hemorrhage
    • Sterile intestines at birth unable to synthesize vitamin K
    • All neonates routinely given Vitamin K injection at birth
  • Easy bleeding (e.g. from gums) and bruising is seen in adults
• Laboratory findings
  • increased PT (most important)
    • most affected due to factor VII deficiency
    • corrects with vitamin K supplementation
  • increased aPTT (less important)
    • Vitamin K also affects common pathway (factors II, IX, X)
  • normal bleeding time
    • due to unaffected platelet function

Find Vitamin K Deficiency and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.