Medicine & USMLE

Vitamin K Deficiency

  1. Vitamin B1 (Thiamine) Biochemistry
  2. Vitamin B1 (Thiamine) Deficiency
  3. Vitamin B2 (Riboflavin)
  4. Vitamin B3 (Niacin) Biochemistry
  5. Vitamin B3 (Niacin) Deficiency and Excess
  6. Hartnup Disease
  7. Vitamin B5 (Pantothenic Acid)
  8. Vitamin B6 (Pyridoxine)
  9. Vitamin B7 (Biotin)
  10. Vitamin B9 (Folate)
  11. Vitamin B12 (Cobalamin) Biochemistry
  12. Vitamins B9 and B12 Deficiencies
  13. Vitamin A (Retinol) Biochemistry
  14. Vitamin A (Retinol) Deficiency and Excess
  15. Vitamin C (Ascorbic Acid) Biochemistry
  16. Vitamin C (Ascorbic Acid) Deficiency and Excess
  17. Vitamin D Biochemistry
  18. Vitamin D Deficiency and Excess
  19. Vitamin E (Tocopherol/Tocotrienol)
  20. Vitamin K Biochemistry
  21. Vitamin K Deficiency
  22. Zinc
  23. Kwashiorkor and Marasmus


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.