Plasma ascorbic acid: measurement, stability and clinical utility revisited

Area of Science:

• Clinical Chemistry
• Biochemistry
• Analytical Chemistry

Background:

• Accurate measurement of plasma ascorbic acid is crucial for nutritional and clinical assessments.
• Existing methods like High-Performance Liquid Chromatography (HPLC) can be time-consuming.
• Investigating alternative assays and optimal sample handling is essential for efficient diagnostics.

Purpose of the Study:

• To compare the performance of the colorimetric FRASC assay against the reference HPLC method for plasma ascorbic acid determination.
• To evaluate the stability of plasma ascorbic acid under various anticoagulant and storage conditions.
• To assess the impact of different anticoagulants on ascorbic acid measurements.

Main Methods:

• Plasma samples (n=31) were analyzed using both FRASC and HPLC methods for direct comparison.
• Plasma stability was assessed using matched samples with EDTA, heparin, citrate, and fluoride/oxalate.
• Samples were stored under varied time and temperature conditions to simulate real-world scenarios.

Main Results:

• The FRASC assay demonstrated comparable precision, limit of detection, and recovery to HPLC.
• Results from FRASC and HPLC methods were statistically indistinguishable (mean difference: 1.8 µmol/L).
• Ascorbic acid exhibited greatest stability in heparinized plasma, while significant degradation was observed in EDTA plasma within 30 minutes.

Conclusions:

• The FRASC assay provides a rapid and dependable alternative to HPLC for quantifying plasma ascorbic acid.
• Heparin is recommended as the anticoagulant of choice to preserve ascorbic acid integrity.
• Prompt analysis or appropriate anticoagulant selection is vital due to rapid ex vivo degradation in EDTA plasma.