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Clinical Chemistry, Vol 31, 1703-1705, Copyright © 1985 by American Association for Clinical Chemistry
AH Chalmers, DM Cowley and BC McWhinney
Ascorbate is unstable in urine at room temperature at pH values ranging from 1 to 12. At pH 7 and above, oxalate is generated in amounts directly proportional to the ascorbate concentration. In 12 different urines, adjusted to pH 12 and incubated for 20 h at room temperature, there was a significant correlation between the amount of oxalate formed and the initial ascorbate concentration (r = 0.97, p less than 0.01). The mean (+/- SD) concentration of oxalate (1.32 +/- 0.70 mmol/L) formed during this period approximated the initial ascorbate concentration (1.57 +/- 1.09 mmol/L). Disodium EDTA, 10 mmol/L final concentration, stabilizes ascorbate in urine and inhibits its conversion to oxalate at pH values of 4.4 to 7.0 during a 24-h period. We therefore propose that urine specimens for ascorbate and oxalate analyses be collected with disodium EDTA present such as to give about this final concentration.
The following articles in journals at HighWire Press have cited this article:
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L. P. de la Vega, J. C. Lieske, D. Milliner, J. Gonyea, and D. G. Kelly Urinary Oxalate Excretion Increases in Home Parenteral Nutrition Patients on a Higher Intravenous Ascorbic Acid Dose JPEN J Parenter Enteral Nutr, November 1, 2004; 28(6): 435 - 438. [Abstract] [Full Text] [PDF] |
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