Vitamin K Deficiency: Diagnosis and Management.

Vitamin K (VK) deficiency (VKD) commonly causes coagulopathy across the age spectrum. The reduced form of VK is an essential cofactor for the post-translational γ-carboxylation of coagulation factors (Fs) II, VII, IX, and X; proteins C and S; and additional proteins. This carboxylation creates high-affinity calcium-binding sites that are important for their functions. VK is a fat-soluble vitamin, with half of the daily needs met by vitamin K1 from the diet (particularly green leafy vegetables) and the other half met by vitamin K2 produced by gut flora. VKD can develop within days because of limited tissue stores of VK. VKD increases risks for bleeding, with neonates and infants at the highest risk unless they are administered routine VK prophylaxis at birth. Diagnosing VKD is challenging because of the different forms and half-lives of VK isoforms. Often, patients with suspected VKD-related coagulopathies are assessed for coagulopathy correction within 1-2 days after receiving VK, either orally or parenterally. VKD increases the plasma levels of proteins induced by the absence of VK, such as des-γ-carboxylated factor II, which is more commonly used as a biomarker for hepatocellular carcinoma than as a VKD biomarker. VKD causes notable discrepancies in FII levels measured by factor assays based on the prothrombin time (PT) rather than Ecarin reagents, as the Ecarin prothrombin activator directly converts normal and des-γ-carboxylated FII to meizothrombin (resulting in higher FII levels than estimated with PT reagents). In this review, we summarize current information on the causes, consequences, diagnosis, prevention, and treatment of VKD.