Advances in Analysis of Urinary Oxalate: The Ascorbate Problem Solved

  • G. A. Rose


Urinary oxalate is more critical than urinary calcium for calcium urolithiasis1, but still not measured in most laboratories. Despite many new recent methods (Table 1), none has found general acceptance2−5. One particular difficulty concerns ascorbate. In 1933, it was reported that ascorbic acid could be oxidised to oxalate6. Stage 1, thought to be oxidation of ascorbate to dehydroascorbate, is catalysed by nitrite and by Fe3+. In steps 2 and 3 (alkaline pH only), the latter converts to 2,3-diketogulonate and then to oxalate plus threonate. This important fact, forgotten for 50 years, was rediscovered simultaneously elsewhere7 and here. Since several promising methods have used alkaline conditions, serious errors could be introduced by ascorbate in urine, particularly in the summer time when several mmols per day may be present. We have therefore investigated this conversion in a number of methods and found ways of preventing it. Fortunately, the oxalate decarboxylase method2, operates at pH 3.5, where physiological ascorbate in urine does not yield detectable oxalate and it can be used as a reference method for studying the conversion. Figs. 1 and 2 show the conversion of ascorbate to oxalate under various conditions of time and pH. Fortunately, methods of preventing these conversions have recently been found. In the presence of oxygen, nitrite catalyses the oxidation of ascorbate to dehydroascorbate8, which is stable in acid, but not in alkaline conditions. Fe3+ forms an unstable complex with ascorbate which quickly converts to Fe2+ and dehydroascorbate9. Rather surprisingly, and for reasons unknown, ferric chloride prevents conversion of ascorbate to oxalate. Perhaps the iron forms a stable complex with the intermediate diketogulonate.


Urinary Oxalate Oxalate Concentration Oxalate Oxidase Oxalate Oxalate Unstable Complex 


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  1. 1.
    W. G. Robertson and M. Peacock, Nephron 26:105 (1980).PubMedCrossRefGoogle Scholar
  2. 2.
    P. C. Hallson and G. A. Rose, Clin. Chim. Acta 55:29 (1974).PubMedCrossRefGoogle Scholar
  3. 3.
    G. A. Rose “Urinary Stones-.Clinical and Laboratory Aspects”, MTP Press, Lancaster (1982).Google Scholar
  4. 4.
    A. Hodgkinson. “Oxalic Acid in Biology and Medicine”, Academic Press, London (1977).Google Scholar
  5. 5.
    G. A. Rose, W. G. Robertson, and R. W. E. Watts, eds., “Oxalate in Human Biochemistry and Clinical Pathology”. Wellcome Foundation, London (1979).Google Scholar
  6. 6.
    R. W. Herbert, E. L. Hirst, E. G. U. Percival, R. J. W. Reynolds, and F. Smith, J. Chem. Soc. 1270 (1933).Google Scholar
  7. 7.
    J. E. Buttery, N. Ludvigsen, E. Braiotta, and R. R. Pannall, Clin. Chem. 29:700 (1983).PubMedGoogle Scholar
  8. 8.
    C. L. Walters,:in: “Ascorbic Acid:Chemistry, Metabolism and Uses”, R. A. Seib and B. M. Tolbert, eds., Amer. Chem. Soc. Adv. in Chem. 200 (1982).Google Scholar
  9. 9.
    G. S. Lawrence and K. J. Ellis, J. Chem. Soc. 1667 (1972).Google Scholar
  10. 10.
    M. Menon and C. J. Mahle, Clin. Chem. 29:369 (1983).PubMedGoogle Scholar
  11. 11.
    J. Chiriboga, Arch. Biochem. Biophys. 116:516 (1966).PubMedCrossRefGoogle Scholar
  12. 12.
    M. F. Laker, A. F. Hofmann, and B. J. D. Meeuse, Clin. Chem. 26:827 (1980).PubMedGoogle Scholar
  13. 13.
    D. M. Obzansky and K. E. Richardson, Clin. Chem. 29:1815 (1983).PubMedGoogle Scholar
  14. 14.
    N. Potezny, R. Bais, P. D. O’Loughlin, J. B. Edwards, A. M. Rofe, and R. J. Conyers, Clin. Chem. 29:16 (1983).PubMedGoogle Scholar
  15. 15.
    M. Hatch, Bourke, E., and J. Costello, Clin. Chem. 23:76 (1977).Google Scholar
  16. 16.
    H. Hughes, L. Hagen, and R. A. L. Sutton, Analyt. Biochem. 119: 1 (1982).PubMedCrossRefGoogle Scholar
  17. 17.
    N. Fituri, N. Allawi, M. Bentley, and J. Costello, Eur. Urol. 9:312 (1983).PubMedGoogle Scholar
  18. 18.
    A. DiCorcia, R. Samperi, G. Vinci, and G. O’Ascenzo, Clin. Chem. 28:1457 (1982).Google Scholar
  19. 19.
    B. G. Wolthers, and M. Hayer, Clin. Chim. Acta 120:87 (1982).PubMedCrossRefGoogle Scholar
  20. 20.
    C. J. Farrington and A. H. Chalmers, Clin. Chem. 25:1993 (1979).PubMedGoogle Scholar
  21. 21.
    D. J. Tocco, A. E. W. Duncan, R. M. Noll, and D. E. Duggan, Analyt. Biochem. 94:470 (1979).PubMedCrossRefGoogle Scholar
  22. 22.
    W. Tschope, R. Brenner, and E. Ritz, J. Chromatog. 222:41 (1981).CrossRefGoogle Scholar
  23. 23.
    N. Schwendtner, W. Achilles, W. Engelhardt, P. O. Schwüle and A. Sigel, J. Clin. Chem. Clin. Biochem. 20:833 (1982).PubMedGoogle Scholar
  24. 24.
    G. G. Mayer, D. Markow, and F. Karp, Clin. Chem. 9:334 (1963).PubMedGoogle Scholar
  25. 25.
    J. D. Sallis, M. F. Lumley, and J. E. Jordan, Biochem. Med. 18:371 (1977).PubMedCrossRefGoogle Scholar
  26. 26.
    M. Bishop, H. Freudiger, U. Largiader, J. D. Sallis, R. Felix, and H. Fleisch, Urol. Res. 10:191 (1982)PubMedCrossRefGoogle Scholar
  27. 27.
    D. J. Bennett, F. E. Cole, E. D. Fröhlich, and D. T. Erwin, J. Lab. Clin. Med. 91:822 (1978).PubMedGoogle Scholar
  28. 28.
    R. K. Kobos and T. A. Ramsey, Anal. Chim. Acta. 121:111 (1980).CrossRefGoogle Scholar
  29. 29.
    G. Kohlbecker, L. Richter, and M. Butz, J. Clin. Chem. Clin. Biochem. 17:309 (1979).PubMedGoogle Scholar
  30. 30.
    T. D. R. Hockaday, E. W. Frederick, J. E. Clayton, and L. H. Smith, L. Lab. Clin. Med. 65:677 (1965).Google Scholar
  31. 31.
    D. A. Gibbs and R. W. E. Watts, J. Lab. Clin. Med. 732:901 (1969).Google Scholar
  32. 32.
    S. Johansson and R. Tabova, Biochem. Med. 11:1 (1974)PubMedCrossRefGoogle Scholar
  33. 33.
    O. P. Foss, “In Vitro Procedures with Radioisotopes in Medicine”, IAEA, Vienna (1969).Google Scholar
  34. 34.
    D. E. Duggan, R. W. Walker, R. M. Noll, and W. J. A. Vandenheuval, Analyt. Biochem. 94:477 (1979).PubMedCrossRefGoogle Scholar
  35. 35.
    J. Yriberri and S. Posen, Clin. Chem. 26:881 (1980).PubMedGoogle Scholar

Copyright information

© Plenum Press, New York 1985

Authors and Affiliations

  • G. A. Rose
    • 1
  1. 1.The Institute of UrologySt Peter’s HospitalsLondonUK

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