Assessment of Vitamin K Nutritional Status

The usual method of assessing vitamin K nutritional status, or monitoring the efficacy of anticoagulant therapy, is a functional test of blood clotting, and hence the ability to synthesize the vitamin K-dependent clotting factors. 

The standard assay measures the time taken for the formation of a fihrin clot in citrated plasma after the addition of calcium ions and thromhoplastin to activate the extrinsic clotting system - the prothrombin time. The normal prothrombin time is 11 to 13 seconds greater than 25 seconds is associated with severe bleeding. 

Preprothrombin can be determined immunologically, either using antiprothrombin antibodies, after adsorption of the y -carboxylated protein onto barium carbonate or using anti-preprothrombin antibodies that do not cross-react with prothrombin. Circulating concentrations of preprothrombin in vitamin K deficiency are of the order of 150 to 1,500 nmol per L. If elevated preprothrombin is because of vitamin K deficiency, then it will fall on administration of the vitamin, whereas if it is the result of liver disease, then vitamin K supplements will have no effect. 

In deficiency, there is also undercarboxylated osteocalcin in the circulation, and this provides a more sensitive index of marginal status it is detectable, and responds to supplements of vitamin K, in subjects with normal clotting time and no circulating preprothrombin (Sokoll and Sadowski, 1996 Binkley et al., 2000). 

Measurement of the plasma concentration of phylloquinone gives some information about stams, but reflects not only intake but also plasma triacyl-glycerol, because most is carried in chylomicrons and chylomicron remnants. The plasma concentration of phylloquinone is higher in older subjects, but the phylloquinone triacylglycerol ratio is lower than in younger people (Booth andSuttie, 1998). 

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Sokoll LJ and Sadowski JA (1996) Comparison of biochemical indexes for assessing vitamin K nutritional status in a healthy adult population. American Journal of Clinical Nutrition 63, 566-73. 

The classical way of assessing vitamin K nutritional status was by determination of prothrombin time. Can you suggest a more sensitive way of detecting marginal vitamin K deficiency ... 

K Shibata. The metabolism of niacin in each organ and the biological method for assessing the nutritional status of niacin in the rats. Vitamins (Japan) 61 39-56, 1987. 

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