Vitamin A is also known as retinol and is an important contributor to accurate eyesight and proper cell function. As a fat-soluble vitamin, it remains in the body for long periods of time and can produce toxic effects if too much builds up. A vitamin A serum test can help diagnose deficiencies or dangerous levels of this nutrient, as well as diseases that prevent the body from absorbing fats and some vitamins correctly. 

Doctors are most likely to recommend a Vitamin A serum test when patients suffer from night blindness, dry hair, skin or eyes, and thickened skin with lesions. Some people with a deficiency of Vitamin A also suffer from ulcerated or damaged eyes and recurring infections. People with too much vitamin A in their bloodstream may have a headache, vomiting or nausea, and feel weak, tired or dizzy. They can also lose hair and weight over time and may suffer from blurred or double vision. Diseases like Chron, irritable bowel syndrome or celiac disease can affect a person's ability to absorb vitamin A from food, producing malnutrition even in people who eat a good diet.

Normal serum levels for vitamin A range from 50 to 200 micrograms per deciliter. 

The best way to get accurate results involves FASTING for 10 hours before the test, drinking only water if necessary. Some retinol-based medications, such as anti-aging treatments, can cause an inaccurate reading on a vitamin A test.