Vitamin A plays key roles in vision, the immune system, and growth and development. Vitamin E is an antioxidant vitamin responsible for inactivating oxygen radicals and preventing tissue damage. Vitamins A and E are fat-soluble and accumulate in the body. It is necessary to monitor the concentrations of these vitamins to identify both deficiency and toxicity. Vitamin A deficiency leads to blindness and toxicity causes severe malaise. Vitamin E deficiency leads to free radical tissue damage which can cause a variety of diseases. Elevated levels of vitamin E decreases vitamin K concentrations leading to blood clotting dysfunction and hemorrhage.