Vitamin A
Vitamin A is a lipid soluble vitamin that is also called retinoic acid. Vitamin A plays an essential role in light detection by the retina and cellular differentiation of epithelial tissues. Together with carotenoids, vitamin A enhances immune function, reducing the consequences of some infectious diseases.
Vitamin A deficiency is rare in the United States, but is a common nutritional deficiency in underdeveloped countries. In the United States, vitamin A deficiency may be seen with disorders causing fat malabsorption such as biliary cholangitis, Crohn disease, and bariatric surgery. Night blindness is an early symptom that may be followed by xerophthalmia, corneal ulcers, scarring, and blindness.
The World Health Organization recommendations supplementation when vitamin A levels fall below 20.0 ug/dL. Severe deficiency is indicated at levels below 10.0 ug/dL.
Vitamin A in excess can be toxic. Chronic vitamin A intoxication can occur in adults who ingest >15 mg per day and children who ingest >6 mg per day over a period of several months. Manifestations include dry skin, cheilosis, glossitis, vomiting, alopecia, bone pain, hypercalcemia, lymph node enlargement, hyperlipidemia, amenorrhea, and pseudotumor cerebri. Vitamin A concentrations >120.0 ug/dL suggest hypervitaminosis A.
Vitamin A is measured in serum by liquid chromatography-tandem mass spectrometry. Specimen requirement is a red top tube of blood.
