Urea Kinetics and Clinical Chemistry Parameters in Patients on Twice-Weekly Hemodialysis

Background Despite the fact that thrice-weekly hemodialysis is regarded as the standard for maintenance dialysis, prescription of twice-weekly hemodialysis with a longer treatment time is common in Hong Kong to allow more renal failure patients to receive treatment. In an attempt to assess whether clinical and biochemical parameters differ between hemodialysis with different interdialytic intervals, we investigated the urea kinetics and blood biochemistry parameters in patients undergoing two dialysis sessions per week. Methods Data were collected for 16 anuric stable maintenance dialysis patients for two dialyses in the same week. Results Compared with hemodialysis after a short interdialytic interval (HD SII ), hemodialysis after a long interdialytic interval (HD LII ) led to significantly greater interdialytic weight gain. Predialysis plasma potassium, urea and creatinine concentrations were significantly higher for HD LII . On the other hand, there were no significant differences in predialysis plasma sodium, chloride, total carbon dioxide, albumin, calcium and phosphorus concentrations and anion gap between HD SII and HD LII . Both immediate postdialysis and 30-minute postdialysis plasma urea concentrations were significantly higher for HD LII . Urea removal, creatinine removal, modified urea reduction ratio (mURR), single-pool Kt/V (spKt/V) and equilibrated Kt/V (eKt/V) were significantly greater for HD LII . Moreover, there was a good linear relationship between mURR for HD SII and HD LII . Similar findings were noted for both spKt/V and eKt/V. However, there were no differences between the two dialyses in urea reduction ratio, normalized protein equivalent of total nitrogen appearance and postdialysis urea rebound. Conclusion Our findings suggest that there are differences in some dialysis indices and blood biochemistry parameters between HD SII and HD LII . Standardization of dialysis sessions (HD SII or HD LII ) for blood sampling schedules is needed to permit meaningful comparison of dialysis indices and biochemistry parameters within and between dialysis patients.