Ascorbic acid is essential for the enzymatic amidation of neuropeptides, production of adrenal cortical steroid hormones, promotion of the conversion of tropocollagen to collagen, and metabolism of tyrosine and folate. It also plays a role in lipid and vitamin metabolism and is a powerful reducing agent or antioxidant. Specific actions include activation of detoxifying enzymes in the liver, antioxidation, interception and destruction of free radicals, preservation and restoration of the antioxidant potential of vitamin E, and blockage of the formation of carcinogenic nitrosamines. Vitamin C promotes collagen synthesis, maintains capillary strength, facilitates release of iron from ferritin to form hemoglobin, and functions in the stress response. In addition, vitamin C appears to function in a variety of other metabolic processes in which its role has not been well characterized.
Normal range: 0.4 " “2.0 mg/dL.
Use
Investigate suspected metabolic or malabsorptive disorders
Investigate suspected scurvy
Interpretation
Decreased In
Alcoholism
Anemia
Cancer
Hemodialysis
Hyperthyroidism
Malabsorption
Pregnancy
Rheumatoid disease
Scurvy
Limitations
Drugs and substances that may decrease vitamin C levels include acetylsalicylic acid, aminopyrine, barbiturates, estrogens, heavy metals, oral contraceptives, nitrosamines, and paraldehyde.
Chronic tobacco smoking decreases vitamin C levels.
Testing of nonfasting specimens or the use of vitamin supplementation can result in elevated plasma vitamin concentrations. Reference values were established in patients who were fasting.
After consuming vitamin C, plasma values rapidly rise within 1 " “2 hours and reach peak concentration within 3 " “6 hours after ingestion.