Human plasma oxalate concentration re-examined.

Area of Science:

• Biochemistry
• Clinical Chemistry
• Analytical Chemistry

Background:

• Accurate measurement of plasma oxalate is crucial for understanding oxalate metabolism and related health conditions.
• Previous in vitro assays for plasma oxalate concentration may overestimate levels due to artifactual oxalate generation.
• Reconciling in vitro and in vivo estimates requires methodological refinement.

Purpose of the Study:

• To modify the radioenzymatic isotope dilution assay (REIDA) for more accurate plasma oxalate concentration measurement.
• To minimize in vitro artifacts that lead to overestimation of plasma oxalate.
• To establish a reliable method for assessing baseline plasma oxalate levels.

Main Methods:

• Modified the radioenzymatic isotope dilution assay (REIDA) by precipitating calcium oxalate from plasma ultrafiltrates within one hour of phlebotomy.
• Utilized 'fire-cleaned' glassware to prevent contamination and artifactual oxalate formation.
• Investigated the effect of inhibitors on glyoxalate to oxalate conversion and compared results between different racial groups.

Main Results:

• The modified REIDA yielded a plasma oxalate concentration of 4.0 mumol/L in normal males, consistent with other validated methods.
• This value is significantly lower than previously reported estimates using older chemical/enzymatic methods.
• No significant differences in plasma oxalate were observed between age-matched black and white males or with the use of glyoxalate conversion inhibitors.

Conclusions:

• The refined REIDA method provides a more accurate assessment of in vivo plasma oxalate concentration.
• The study highlights the importance of minimizing in vitro artifacts in biochemical assays.
• The findings contribute to a better understanding of normal plasma oxalate levels and oxalate metabolism.