Spectrophotometric determination of oxalate in whole blood

Abstract

Whole blood oxalate concentrations have been reported to be higher than serum or plasma concentrations [l-3], however, this has not been confirmed by more recent, reliable methods. Measurement of oxalate in whole blood involves all of the same problems associated with oxalate determination in serum or plasma and the color of blood can provide an additional drawback. Recently, Costello and Landwehr [4] reviewed many methods currently available to measure oxalate concentrations in serum and they note that the discrepancy between values obtained by direct methods and isotope-dilution procedures has narrowed considerably. Mean serum or plasma oxalate concentrations have now been demonstrated to range between 1.25 and 4.01 pmol/l using a variety of enzymic methods [4], while in vivo isotopic studies consistently demonstrate lower mean oxalate values, < 1.83 pmol/l [4]. It can be concluded that reliable determination of serum oxalate is now both possible and necessary in a variety of clinical conditions [4]. The determination of oxalate in whole blood is of interest for many reasons. First, it is not known whether the oxalate concentration in whole blood is higher than serum in healthy normals or in patients with hyperoxalemia. Second, such methodology would appear to be extremely useful in the investigation of the reported oxalate transport defect in red blood cells in idiopathic calcium oxalate nephrolithiasis described by Baggio et al. [5]. Finally, if serum and whole blood oxalate levels are found to be similar then less blood volume would necessarily be required for routine measurements employing current modified serum methods.