Overview
Differentiate correctable vitamin K deficiency from the rebalanced haemostasis of liver disease, investigate bleeding by phenotype, and use vitamin K, components or anticoagulation without treating INR as a complete measure of risk.
Vitamin K is needed to gamma-carboxylate factors II, VII, IX and X and anticoagulant proteins C and S. Deficiency follows inadequate intake combined with illness, fat malabsorption or cholestasis, prolonged antibiotics, pancreatic or biliary disease, or a vitamin K antagonist. The PT becomes prolonged early because factor VII turns over quickly. APTT rises in severe depletion. Platelet count and fibrinogen remain normal unless another process coexists. A response to phytomenadione supports deficiency, but urgent bleeding requires simultaneous treatment rather than a delayed therapeutic trial.
Liver disease is different. Hepatic synthesis of procoagulants falls, but so do protein C, protein S and antithrombin. Factor VIII and VWF are maintained or increased, ADAMTS13 falls, platelets may be low from portal sequestration and thrombopoietin deficiency, and fibrinolysis varies. This creates a vulnerable rebalance that can tip toward bleeding or thrombosis with infection, renal failure, endothelial injury or intervention. INR was standardised for warfarin monitoring and cannot represent this whole system.