From the Guidelines
To measure vitamin C levels, a blood test checking for ascorbic acid concentration in blood serum or plasma is the most accurate method, but it is not recommended in critical illness or severe inflammation due to difficulty in interpreting results. When measuring vitamin C levels, it's essential to consider the context, as plasma vitamin C measurement is not recommended in critical illness or severe inflammation, as stated in the ESPEN micronutrient guideline 1. In general, vitamin C levels can be measured through a blood test, with normal ranges typically between 0.6-2.0 mg/dL, though reference ranges may vary slightly between laboratories 1. Some key points to consider when measuring vitamin C levels include:
- The unit conversion for ascorbic acid is 1 mg/dL = 56.78 mmol/L and 1 mmol/L = 0.0176 mg/dL, as noted in the ESPEN micronutrient guideline 1
- Home test kits are available but are generally less accurate than blood tests
- Monitoring for physical signs of deficiency, such as bleeding gums, slow wound healing, or fatigue, can also be an option, though these symptoms appear only with significant deficiency
- Increasing consumption of vitamin C-rich foods like citrus fruits, bell peppers, and leafy greens can help raise vitamin C levels before formal testing. It's crucial to note that decreased vitamin C levels have been reported in patients with certain medical conditions, such as chronic kidney disease (CKD), and those receiving hemodialysis (HD) or peritoneal dialysis (PD) 1.
From the Research
Methods for Measuring Vitamin C Levels
- Determination of vitamin C levels in blood plasma and/or leukocytes is the current choice for individual and population assessments 2
- High-performance liquid chromatography (HPLC) can be used to determine reduced (ascorbic acid), oxidized (dehydroascorbic acid), or total amounts of vitamin C in biological specimens or foods 2, 3, 4
- Plasma levels of vitamin C forms are easily determined but may not reflect tissue content as well as leukocyte levels 2
- Lymphocyte vitamin C levels provide the most accurate assessment of the true status of vitamin C stores and are not affected acutely by circadian rhythm or dietary changes 3
Analytical Techniques
- Reverse phase HPLC with a UV detection system can be used for the quantification of vitamin C in lymphocytes 3
- The proposed HPLC method offers a reliable and reproducible technique for the quantification of intracellular vitamin C 3
- A reversed-phase HPLC method for ascorbic acid can be used in conjunction with cellular differential centrifugation technique for the determination of ascorbic acid in relatively pure blood cell fractions 4
Sample Preparation and Stability
- Lymphocyte samples can be rapidly prepared and represent a more homogeneous tissue sample source for intracellular vitamin C measurement as compared to serum 3
- To ensure stability, lymphocyte lysates should be prepared and stored at or below -20 degrees C within 2 h of blood collection 3
- Vitamin C was most stable at 4 degrees C, with a 0.31% decrease after 3 h and 2.35% after 4 h 3