Clinical significance
Vitamin A is one of the fat-soluble vitamins and is found in liver, especially fish liver. Vegetables (carrots, spinach, lettuce) and fruit (blueberries, apricots, melon) are rich in carotenoids (e.g. beta-carotene), the precursors of vitamin A; their conversion into retinol (the biologically active form) in intestinal cells is limited, and the excess is stored in subcutaneous fat.
Vitamin A plays an essential role in the pigments of the retina (rhodopsin) and in epithelial tissues in general.
Absorption may be reduced by primary malabsorption (coeliac disease) or secondary malabsorption (liver or pancreatic insufficiency). The main clinical signs involve the eyes (night blindness, xerophthalmia, corneal ulcers) and skin (xerosis, hyperkeratosis), together with greater susceptibility to infections. Overdose can cause skin, intestinal and neurological disorders.
Clinical indications
Primary and secondary deficiency states.
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
Notes
Neomycin and colestyramine reduce its absorption.
Toxic effects may occur with values ≥ 150 µg/L