Vitamin C is also called L-ascorbic acid and L-ascorbate. It is one of the most common essential nutrients and is responsible for keeping the body's metabolism working correctly. Too little vitamin C results in a condition known as scurvy. Since this vitamin is water-soluble and can be excreted over the course of a day or so, cases of vitamin C overdose are very rare. 

A doctor may recommend that patients have a vitamin C test performed if they show signs of brown spots on the skin, spongy tissue around the gums or bleeding from the gums, nostrils or other mucus membranes. People who need to find out about their vitamin C deficiency may also be pale and depressed, with teeth that feel loose or sores that don't heal easily. People who have low levels of this vitamin are also at a higher risk of lung diseases, especially if they smoke. Chronic vitamin C deficiency could contribute to hardening of the arteries.

Measuring vitamin C levels in the bloodstream can be difficult, especially if those levels are very low. Most people should have vitamin C blood levels equivalent to about 0.55 milligrams per deciliter, though higher levels are tolerable. People who show signs of low vitamin C can easily improve their condition by consuming more fresh or dried fruits and vegetables, or by adding supplements to their diet. 

This test requires FASTING for approximately 10 hours to obtain accurate results.