The test measures serum retinol levels.
Vitamin A can be derived through the diet as the preformed retinol and retinyl esters in animal products and also as the precursor beta-carotene in plant foods. A percentage of the population (studies suggest this may be as high as 45%) are however, unable to convert beta-carotene efficiently into vitamin A.
Vitamin A is needed for eye health and also stimulates the growth and activity of white blood cells. It is important for maintaining healthy mucosal surfaces and has a role in bone remodelling and the control of cell division during reproduction.
High levels are toxic.
Mild insufficiency is associated with fatigue, susceptibility to infections and infertility.
Severe deficiency is associated with extreme dry eyes (that can lead to blindness if untreated) night blindness, patches on the whites of the eye, dry skin or hair.