A. Hesse

Experience with the [13C2]Oxalate Absorption Test

Abstract Hyperoxaluria is the most important risk factor for a formation of calcium oxalate-urinary stones. Usually, the bulk of oxalate will be formed in the human body, but in many patients the oxalate from food plays the decisive role. Conventionally, in urine the endogenous oxalate can not be distinguished from food derived oxalate. We have developed a standardized oxalate-absorption test, applying a physiological dose (50 mg disodium salt of [13C2]oxalic acid) of labelled oxalate. The assay has been published. Now we report on the first extensive applications of this test in 86 volunteers and 135 patients from different groups with calcium oxalate stones or an increased risk of the formation of such stones. In one-third of the patients with calcium oxalate-urinary stones an oxalate hyperabsorption was diagnosed. For these patients, a dietetic stone prophylaxis and/or therapy is indicated.

Influence of a low-and a high-oxalate vegetarian diet on intestinal oxalate absorption and urinary excretion

Objective:To compare quantitatively the effect of a low- and a high-oxalate vegetarian diet on intestinal oxalate absorption and urinary excretion.Subjects and methods:Eight healthy volunteers (three men and five women, mean age 28.6±6.3) were studied. Each volunteer performed the [13C2]oxalate absorption test thrice on a low-oxalate mixed diet, thrice on a low-oxalate vegetarian diet and thrice on a high-oxalate vegetarian diet. For each test, the volunteers had to adhere to an identical diet and collect their 24-h urines. In the morning of the second day, a capsule containing [13C2]oxalate was ingested.Results:On the low-oxalate vegetarian diet, mean intestinal oxalate absorption and urinary oxalate excretion increased significantly to 15.8±2.9% (P=0.012) and 0.414±0.126 mmol/day (P=0.012), compared to the mixed diet. On the high-oxalate vegetarian diet, oxalate absorption (12.5±4.6%, P=0.161) and urinary excretion (0.340±0.077 mmol/day, P=0.093) did not change significantly, compared to the mixed diet.Conclusions:A vegetarian diet can only be recommended for calcium oxalate stone patients, if the diet (1) contains the recommended amounts of divalent cations such as calcium and its timing of ingestion to a meal rich in oxalate is considered and (2) excludes foodstuffs with a high content of nutritional factors, such as phytic acid, which are able to chelate calcium.