Assessment of vitamin K status of the newborn infant.

This article reviews our current knowledge of the assessment of vitamin K status in the human infant, where a deficiency state has been described. Laboratory measures for the functional assessment of vitamin K-dependent coagulation factors as well as the quantitative assay for vitamin K1 (phylloquinone) are reviewed. In addition, four different methods of measuring abnormal prothrombin, a protein induced by vitamin K absence (PIVKA-II), and its use in clinical pediatrics are discussed. Finally, additional methods are briefly described for assessing vitamin K status, including serum osteocalcin, urinary excretion of gamma-carboxyglutamic acid, and deficiencies of the enzymes necessary for the regeneration of phylloquinone in the so-called vitamin K cycle.