Vitamin C

Plasma, frozen and protected from light

1 mL

0.5 mL (Note: This volume does not allow for repeat testing.)

Green-top (lithium heparin) tube; amber plastic transport tube with amber-top. (If amber tubes are unavailable, cover standard transport tube completely, top and bottom, with aluminum foil. Identify specimen with patient name directly on the container and on the outside of the aluminum foil. Secure with tape.) For amber plastic transport tube and amber-top, order LabCorp No. 23594.

Along with dietary history, evaluating serum ascorbic acid levels should be considered for patients with classic signs and symptoms of scurvy, as well as for those with common, nonspecific, chronic musculoskeletal complaints. Vitamin C deficiency is generally defined as plasma or serum concentrations less than 0.2 mg/dL, or the the level at which signs and symptoms of scurvy may appear. Serum ascorbic acid concentrations between 0.2 and 0.4 mg/dl are considered low.^2,28,29

This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.

Liquid chromatography-tandem mass spectrometry (LC/MS-MS)

Vitamin C, also referred to as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, fortified in others, and available as a dietary supplement alone or in multivitamins.^1,2 Humans, unlike most animals, cannot synthesize vitamin C de novo and must obtain it as an essential dietary component.^1,3

Vitamin C a is required cofactor for the biosynthesis of a number of critical compounds.^2,8 It is required for the function of several enzymes involved in the production of collagen, an essential component of connective tissue. These enzymes are required for the molecular cross-linking that gives collagen its elasticity. Vitamin C deficiency renders the polypeptide unstable and unable to self-assemble into rigid triple helices. Impaired collagen production can result in poor wound healing and a weakening of collagenous structures leading to tooth loss, joint pains and bone and connective tissue pathology and blood vessel fragility. Vitamin C also serves as a cofactor in the biosynthesis of carnitine, an essential compound for the transport of activated long chain fatty acids into the mitochondria. Vitamin C deficiency related reduction in carnitine levels results in fatigue and lethargy. Vitamin C is an essential cofactor for the conversion of dopamine to norepinephrine and in the metabolism of tyrosine and folate and the conversion of cholesterol to bile acids. In addition, vitamin C in the diet improves the absorption of non-heme iron, the form of iron present in plant-based foods.⁹

Profound and extended vitamin C deficiency leads to scurvy, a condition that is characterized by blood vessel fragility, connective tissue damage, fatigue, and, ultimately, death.^1-13 Early symptoms can include weakness, listlessness, as well as shortness of breath and aching joints, bones and muscles. Myalgias occur because of the reduced production of carnitine. Oral complications can include gingival bleeding with minor trauma that proceeds to alveolar bone absorption and tooth loss. Iron deficiency anemia can also occur due to increased intestinal bleeding and decreased non-heme iron absorption.^10-13 Rheumatologic problems, such as painful hemarthrosis and subperiosteal hemorrhage, may occur.¹² Cardiac enlargement may occur because of congestive heart failure secondary to high-output anemia. Scurvy manifests when vitamin C intake falls below 10 mg/day for many weeks.^10-13 Scurvy is rare in developed countries but can still occur in people with limited food variety and in other high risk groups.

Under physiological conditions, vitamin C serves as a potent antioxidant and has been shown to regenerate other antioxidants, particularly vitamin E.^2,14-16 The reduced form of the vitamin, ascorbic acid, is a very effective antioxidant due to its high electron-donating power and ready conversion back to the active reduced form by glutathione.² This antioxidant action plays a role in limiting the damage caused of free radicals produced by normal metabolic respiration and might serve to deter the development of certain cancers, cardiovascular disease, and other diseases.^2,14-16 Vitamin C concentration has been shown to be inversely associated with all-cause mortality.^17,27 Low plasma vitamin C concentrations are associated with increased blood pressure^16,17 and an increased risk of cardiovascular disease^{9,15,18,21-23} and diabetes.^24,25

The NHANES 2003-2004 revealed that approximately seven percent of the United States population has deficient serum levels of vitamin C (levels below 11 umol/L).²⁸ The prevalence of vitamin C deficiency was markedly higher in smokers relative to nonsmokers, possibly due to the increased catabolism associated with the oxidative stress of caused by smoking.^2,28 Lower vitamin C levels are seen in the institutionalized elderly, possibly due to clinical conditions such as recurrent infections.² Levels are also lower in low-income compared with the high-income persons.²⁸ Other at-risk groups include persons with gastroinestinal disease or poor dentition.^2,12 Cancer patients on chemotherapy who have increased nausea and diarrhea are also at risk, as are patients on hemodialysis.¹² Psychiatric disorders including depression, schizophrenia, or anorexia, also can put patients at risk for reduced intake of vitamin C.¹² Alcoholic persons are at risk for scurvy because they may have poorly balanced diets and because decreases the absorption of vitamin C.¹²