Vitamin C Testing Guidelines

Sample Collection and Processing

Plasma samples must be collected using lithium heparin tubes to ensure accurate vitamin C analysis 1, 2
Immediate processing is essential due to vitamin C's high susceptibility to degradation, requiring centrifugation at 4°C and prompt plasma separation after blood drawing 1, 2, 3, 4
Samples require protection from light exposure throughout the entire workflow and storage at ultra-low temperature (-70 to -80°C) to maintain stability 1, 2, 4

High-Performance Liquid Chromatography (HPLC) is the gold standard method for vitamin C analysis, which can be performed with ultraviolet (UV), fluorescence, or electrochemical detection 1, 2
HPLC requires acidification followed by immediate cold storage at ultra-low temperature and can measure both L-ascorbic acid (AA) and its oxidation product dehydroascorbic acid (DHAA) 1, 2, 4
Total vitamin C analysis typically involves the addition of a reducing agent to convert DHAA into AA, and DHAA can be determined by subtracting AA levels before reduction from total vitamin C 1, 2, 4

Vitamin C plasma levels decline rapidly with inflammation, making interpretation difficult, and blood levels decrease when C-reactive protein (CRP) >10 mg/L 1, 4
Normal values are typically not detected if CRP >40 mg/L, and measurement of plasma vitamin C is not recommended during critical illness or severe inflammation due to interpretation difficulties 1, 4, 5, 6

Testing is recommended in patients with clinical suspicion of scurvy or chronic low intake, and a clinical trial of vitamin C should not be delayed if clinical symptoms of deficiency are present 5, 6

Serum determination should be avoided due to poorer reliability, and leukocyte vitamin C testing has significant practical limitations, including requiring more sample volume and involving more complex preanalytical steps 1, 2, 3