Specimen Information

Type

Gold, SST

Volume

1.0 ml

Transport Info

Centrifuge and immediately transfer serum to separate light protected or foil wrapped plastic tube
Frozen

Fasting Required?

True

Clinical Significance

Quantitation of circulating Vitamin A (retinol) concentration
Vitamin A (retinol) is a fat-soluble vitamin that is required for proper vision, growth and normal tissue development. The earliest clinical manifestation of Vitamin A deficiency is vision loss in dim light (night blindness). Two sources of Vitamin A in the diet include preformed vitamin A that is most often present in the form of retinyl ester and the carotenoids (including beta-carotene). They are subject to emulsification and mixed micelle formation by the action of bile salts before being transported into the intestinal cell. The efficiency of absorption of preformed vitamin A is high at between 70–90%. Carotenoids are absorbed into the duodenal mucosal cells by passive diffusion and their absorption efficiency is much lower at between 9 to 22%. Preformed vitamin A is obtained from animal-derived foods, such as organ meats and fish oils. Other sources are full cream milk, butter and fortified margarines. The carotenoids are obtained from yellow to orange pigment fruits and vegetables and green leafy vegetables, such as pumpkin, carrots, tomatoes, apricots, grapefruit, lettuce and most green vegetables. The U.S. National Health and Nutrition Examination Survey (NHANES-II) indicated that approximately 25% of the vitamin A requirement was provided by carotenoids and about 75% by preformed retinol. Vitamin A deficiency can be seen secondary to lack of dietary preformed Vitamin D and carotenoids in malnutrition or lack of adequate intestinal absorption (malabsorption ).

Excess of Vitamin A can lead to toxicity with nausea and vomiting, anorexia, weakness and dermatitis. Skeletal abnormalities can occur in children with Vitamin A toxicity. Ingestion of large amounts of liver (where considerable Vitamin A is stored) can lead to toxicity. Polar bear liver has toxic amounts of Vitamin A.

Measuring the plasma concentration of vitamin A is the most convenient and widely used method to assess vitamin A status. However, it is not an ideal indicator because it does not decline until liver stores become critically depleted.