Improved clearance of iohexol with longer haemodialysis despite similar Kt/V for urea

Nephrol Dial Transplant. 1999 Oct;14(10):2407-12. doi: 10.1093/ndt/14.10.2407.


Background: The efforts to improve the quality of haemodialysis (HD) has renewed the interest in the consequences of blood-flow distribution for removal of solutes.

Methods: To test the effects of HD time per se, 10 patients were studied in a cross-over fashion with HD for 3 h and 1 week later for 6 h, with similar blood urea Kt/Vs, achieved by adjusting the blood flow rate to 290 and 120 ml/min respectively. Injections of iohexol (MW 821 Dalton) were given 2 days prior to the dialysis sessions. Blood samples were taken before, during (6/HD), 1 and 24 h after the HD and analysed for concentrations of urea and iohexol. A urea on-line monitor (Gambro) was used for continuous recordings and sampling of dialysate.

Results: According to the study design the blood Kt/V for urea (Daugirdas II) was similar for 3 and 6 h HD, close to 1.0 (n.s), while the removed mass of urea showed that Kt/V was slightly and significantly higher for the 6 h HD. The 'apparent' mass of iohexol, defined as plasma concentration times estimated distribution volume, fell to 29% and 21% of pre-dialysis levels after 3 h and 6 h HD, respectively (P<0.01), but increased after HD, and more so after the short dialysis, reaching 46% of the predialysis mass 24 h after 3 h HD vs. 36% after 6 h HD (P<0.05). The removed mass of iohexol was 920+/-110 mg with 6h HD and 700+/-81 mg with 3h HD, (P<0.01). Thus, the longer dialysis removed 32% more iohexol despite similar blood Kt/V for urea.

Conclusion: The treatment time per se affects solute removal despite similar blood Kt/V for urea. This is particularly true for an intermediate-size molecule like iohexol.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Contrast Media / analysis
  • Contrast Media / pharmacokinetics*
  • Female
  • Humans
  • Iohexol / analysis
  • Iohexol / pharmacokinetics*
  • Male
  • Middle Aged
  • Osmolar Concentration
  • Renal Dialysis*
  • Time Factors
  • Urea / blood*


  • Contrast Media
  • Iohexol
  • Urea