Plasma ascorbic acid: measurement, stability and clinical utility revisited.
OBJECTIVE
To compare plasma ascorbic acid results by the colorimetric FRASC (Ferric Reducing/Antioxidant and Ascorbic Acid) assay and a reference HPLC method; to re-examine plasma ascorbic acid stability, and anticoagulant effect.


METHODS
For method comparison, 31 plasma samples were tested by both methods. For stability, matching EDTA, heparin, citrate and fluoride/oxalate plasma, stored under different conditions of time and temperature, was measured.


RESULTS
FRASC is an acceptable alternative to HPLC for plasma ascorbic acid: precision, limit of detection and recovery were similar, and results by the two methods were indistinguishable: mean (95% CI) difference:1.8 (-1.1-4.6; n = 31) micromol/L. Ascorbic acid was most stable in heparinized plasma. Marked loss (p < 0.05) in EDTA plasma occurred within 30 min of blood collection.


CONCLUSIONS
FRASC offers a speedy and reliable alternative to HPLC for plasma ascorbic acid. Heparin is proposed as the anticoagulant of choice; loss of ascorbic acid is rapid in EDTA plasma ex vivo.
Chung
W Y
WY
Department of Nursing and Health Sciences, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China.
Chung
J K
JK
Szeto
Y T
YT
Tomlinson
B
B
Benzie
I F
IF
D000328:Adult; D000368:Aged; D000925:Anticoagulants / Q000378:metabolism; D001205:Ascorbic Acid / Q000097:blood* / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D004355:Drug Stability; D004492:Edetic Acid / Q000378:metabolism; D005260:Female; D005290:Ferric Compounds / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry*; D006493:Heparin / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction
D000925:Anticoagulants; D005290:Ferric Compounds; D005609:Free Radicals; D006493:Heparin; D004492:Edetic Acid; D001205:Ascorbic Acid