PURPOSE: It has been suggested that ionic dialysance (ID) can adequately estimate the "effective" urea clearance (eK), i.e. urea clearance corrected for total (access and cardiopulmonary) recirculation. Unfortunately, the results obtained by different authors in determining the relationship existing in vivo between ID and eK do not always agree. Furthermore, it has been recently evidenced that ID values could be different, according to the different methods used to modify the inlet dialysate conductivity during ID measurement. OBJECTIVE: We aimed to verify the relationship between the mean values of repeated instantaneous ID determinations and the urea clearance values corrected for access recirculation, urea clearance corrected for total recirculation (eK) and urea clearance corrected for both total recirculation and post-dialysis urea rebound (body urea clearance), determined according to the direct quantification method (dKDDQ, eKDDQ and bK, respectively). METHODS: Thirty-one anuric patients on chronic thrice-weekly hemodialysis (HD) were studied in 31 dialysis sessions (one per patient), performed using Integra machines equipped with the Diascan module for the automatic ID determination and the Quantiscan module for the fractional collection of outlet dialysate. The mean values of repeated ID determinations at 30 min intervals throughout each dialytic session by the Diascan module were compared with dKDDQ, eKDDQ and bK values. RESULTS: ID = 179 +/- 24 mL/min; dKDDQ = 200 +/- 27 mL/min; eKDDQ = 188 +/- 26 mL/min; bK = 165 +/- 25 mL/min. The mean (ID - dKDDQ) difference was -21 +/- 10 mL/min (95% confidence interval (95% CI) -25 to -17 mL/min; p<0.001). The mean ID/dKDDQ ratio was 0.90 +/- 0.05, indicating a mean difference between dKDDQ and ID of 10%. The mean (ID - eKDDQ) difference was -9 +/- 9 mL/min (95% CI -12 to -6 mL/min; p<0.001). The mean ID/eKDDQ ratio was 0.96 +/- 0.05; therefore, indicating a mean difference between eKDDQ and ID of only 4%. The mean (ID - bK) difference was 15 +/- 7 mL/min (95% CI 13 to 17 mL/min; p<0.001). The mean ID/bK ratio was 1.09 +/- 0.05, indicating a mean difference between bK and ID of 9%. CONCLUSIONS: The mean value of repeated ID determinations could be considered clinically as an adequate estimate of urea clearance corrected for total recirculation (eKDDQ). Given that ID determination does not require either blood sampling or laboratory tests, therefore, it becomes possible to estimate easily and rapidly, once the urea distribution volume (V) has been correctly determined, the Kt/Vsp at each dialytic session.