Vitamin K is a lipid-soluble vitamin absorbed in the terminal ileum and found predominantly in green leafy vegetables or synthesized by colonic bacteria. It is responsible for the synthesis of coagulation proteins.

*In neonates, vitamin K deficiency is a potentially life-threatening emergency.*

Infants are at highest risk for vitamin K deficiency due to low levels of transmission across the placenta, low levels in breast milk, and inefficient production of vitamin K in the colon due to low levels of colonic bacteria. Infants with vitamin K deficiency present with hemorrhagic disease of the newborn at days 1-7 of life with intracranial or retroperitoneal hemorrhage, petechiae, or mucosal bleeding. An acute form associated with maternal medications that inhibit vitamin K synthesis (some antiepileptic agents) may present in the first 48 hours of life, and a delayed form can be seen out to several months from birth, generally exclusively in breast-fed babies whose parents decline to use prophylactic vitamin K supplementation.

In adults, vitamin K deficiency is generally due to dietary insufficiency or malabsorption syndromes. Conditions such as celiac disease, cystic fibrosis, ulcerative colitis, short gut syndrome, primary sclerosing cholangitis, and primary biliary cholangitis can impair absorption. Chronic antibiotic use and total parenteral nutrition (TPN) dependence are other causes. Adults with vitamin K deficiency present with easy bleeding, mucosal bleeding, or easy bruising.