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Laboratory assessment of vitamin K status
  1. David John Card1,
  2. Renata Gorska1,
  3. Dominic Jon Harrington1,2
  1. 1 Nutristasis Unit, Viapath, Guy’s and St. Thomas’ NHS Foundation Trust, London, UK
  2. 2 Faculty of Life Sciences and Medicine, King’s College London, London, UK
  1. Correspondence to Dr Dominic Jon Harrington, Nutristasis Unit, Viapath, Guy’s and St. Thomas’ NHS Foundation Trust, London SE1 7EH, UK; Dominic.Harrington{at}viapath.co.uk

Abstract

Vitamin K is required for the ɣ-carboxylation of specific glutamic acid residues within the Gla domain of the 17 vitamin K-dependent proteins (VKDPs). The timely detection and correction of vitamin K deficiency can protect against bleeding. Vitamin K also plays a role in bone metabolism and vascular calcification. Patients at increased risk of vitamin K deficiency include those with a restricted diet or malnutrition, lipid malabsorption, cancer, renal disease, neonates and the elderly. Coagulation assays such as the prothrombin time have been used erroneously as indicators of vitamin K status, lacking sufficient sensitivity and specificity for this application. The measurement of phylloquinone (K1) in serum is the most commonly used marker of vitamin K status and reflects abundance of the vitamin. Concentrations <0.15 µg/L are indicative of deficiency. Disadvantages of this approach include exclusion of the other vitamin K homologues and interference from recent dietary intake. The cellular utilisation of vitamin K is determined through measurement of the prevalence of undercarboxylated VKDPs. Most commonly, undercarboxylated prothrombin (Protein Induced by Vitamin K Absence/antagonism, PIVKA-II) is used (reference range 17.4–50.9 mAU/mL (Abbott Architect), providing a retrospective indicator of hepatic vitamin K status. Current clinical applications of PIVKA-II include supporting the diagnosis of vitamin K deficiency bleeding of the newborn, monitoring exposure to vitamin K antagonists, and when used in combination with α-fetoprotein, as a diagnostic marker of hepatocellular carcinoma. Using K1 and PIVKA-II in tandem is an approach that can be used successfully for many patient cohorts, providing insight into both abundance and utilisation of the vitamin.

  • nutrition
  • bleeding disorders
  • coagulation
  • bone
  • calcium metabolism
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Footnotes

  • Handling editor Tahir S Pillay.

  • Twitter @DrDJHarrington

  • Contributors All the writing presented here is the original work of the authors.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Commissioned; externally peer reviewed.

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