Plasma Profiles and Dialysis Kinetics of Oxalate in Patients Receiving Hemodialysis

Abstract

Regular dialysis treatment (RDT) does not obviate hyperoxalemia of chronic renal failure (CRF). However, there is emerging evidence suggesting that current dialysis prescription is not always associated to progressive oxalate accumulation. In view of the controversy still concerning this issue, we have investigated on plasma profiles and dialysis kinetics of oxalate in patients on RDT. Oxalate was determined by ion chromatography on serum ultrafiltrates and on the whole dialyzate in 23 stable patients on RDT for end-stage renal failure unrelated to primary hyperoxaluria. Nine patients were on traditional hemodialysis (HD) and 14 on soft hemodiafiltration (HDF). Dialysis prescription was set so as to obtain similar KT/V of urea. Mean dialyzer clearance of oxalate (Kd_Ox) was calculated by standard procedures and was compared to urea (Kd_Urea) and creatinine (Kd_Cr) clearances. Oxalate removal was measured on the whole spent dialyzate. Distribution volume of oxalate (V_Ox) was estimated by assuming a single-pool model and was used to estimate the oxalate appearance rate (OxAR). Plasma profiles showed that dialysis patients were virtually always hyperoxalemia However, the threshold of supersaturation for calcium oxalate was exceeded in only 13 of 138 (9.4%) assayed ultrafiltrates, 13% on HD and 7.1% on HDF. Dialysis reduced plasma oxalate by more than 60%. There was a postdialysis oxalate rebound averaging 9.6% at 30 min from the end of dialysis. Plasma oxalate predialysis was independent of sex, age and time on dialysis. Kd_Ox was mildly higher on HDF than on HD, and was lower than both Kd_Urea and Kd_Cr, irrespective of the dialysis technique. Estimated V_Ox was 21.5 litres, that is 37.3% of dry body weight, and was quite similar to estimates obtained in normal subjects and in patients with CRF by alternative isotope dilution methods. OxAR averaged 337 ± 69 μmol/24 h and was not different from the daily oxalate excretion assessed in 40 healthy subjects by the same oxalate assay. OxAR was independent of sex, age and body weight and was significantly related to urea generation and protein catabolic rates. From our results we conclude that, unless the metabolic generation of oxalate is increased, current dialysis programs should prevent progressive oxalate accumulation in the majority of the patients.

Oxalate Quantification in Hemodialysate to Assess Dialysis Adequacy for Primary Hyperoxaluria

“…Oxalate is reasonably well-removed by dialysis (clearance about 75% that of urea) [18], as evidenced by the correlation of KT/V with fall in plasma oxalate levels. Even so, the amount removed in a standard 3 day per week hemodialysis regimen cannot keep up with production rates [18], in part because oxalate is only removed from the blood compartment, and equilibration of plasma oxalate with extravascular compartments like bone is slower.…”

“…Even so, the amount removed in a standard 3 day per week hemodialysis regimen cannot keep up with production rates [18], in part because oxalate is only removed from the blood compartment, and equilibration of plasma oxalate with extravascular compartments like bone is slower. These considerations likely explain the poor correlation of KT/V with total oxalate removal.…”

The primary hyperoxalurias

“…Plasma oxalate levels in PH-ESRF patients are almost always higher (> 60–100 µmol/l) than those of non-PH-ESRF patients (20–60 µmol/l, [9]). An elevated plasma glycolate or glycerate level may be helpful for distinguishing PH type I from type II disease [19, 20]. The diagnosis can be confirmed by determination of AGT and GRHPR enzyme activity in tissue from a percutaneous liver biopsy.…”

A patient with Primary Hyperoxaluria who developed excessive pericardial effusion despite intensive dialysis

“…All this general precautions are effective before established CKF, but in CKF patients renal replacement therapies should be considered. Oxalate is reasonably well-removed by dialysis, even so, the amount removed in a standard 3 day per week HD treatment can not keep up with production rates, in part because oxalate is only removed from the blood compartment, and equilibration of plasma oxalate with extravascular compartments like bone is slower [13]. Thus, more frequent HD treatment are more efficient than longer but less frequent HD regimens [14].…”