Complex Compartmental Behavior of Small Water-Soluble Uremic Retention Solutes: Evaluation by Direct Measurements in Plasma and Erythrocytes
Received 22 December 2006; accepted 18 May 2007. published online 05 July 2007.
Refers to article:
The Kinetic Behaviors of Urea and Other Marker Molecules During Hemodialysis
Edmund G. Lowrie
American Journal of Kidney Diseases
August 2007 (Vol. 50, Issue 2, Pages 181-183) Full Text |
Full-Text PDF (64 KB)
Background
Although scanty data suggest that large solutes show kinetic behavior different from urea, there are virtually no data comparing the kinetics of urea with those of other small water-soluble uremic compounds, which are believed to behave similarly.
Study Design
Cross-sectional study of kinetics of urea and guanidino compounds in plasma and erythrocyte compartments during a single hemodialysis session.
Setting & Participants
Six stable hemodialysis patients on standard low-flux dialysis therapy.
Predictors
Reduction ratios (RRs) of urea calculated from plasma and erythrocyte concentrations.
Outcomes
RRs for guanidino compounds calculated from measurements of both plasma and erythrocyte concentrations.
Measurements
Blood samples were collected from the dialyzer inlet and outlet at 0, 5, 15, 30, and 120 minutes and at the end of the session. Plasma and erythrocyte concentrations of urea and guanidino compounds (creatinine [CTN], guanidinosuccinic acid [GSA], guanidinoacetic acid [GAA], guanidine [G], and methylguanidine [MG]) were determined.
Results
Postdialysis plasma RR was higher for GSA (82% ± 3%) compared with urea (77% ± 2%; P < 0.01), whereas CTN (69% ± 4%), GAA (49% ± 14%), G (55% ± 7%), and MG (55% ± 7%) showed smaller RRs (P < 0.01). In erythrocytes, GSA (45% ± 1%), G (10% ± 13%), and MG (27% ± 10%) showed markedly smaller RRs than urea (59% ± 6%; P < 0.05). Finally, significant differences were found between plasma and erythrocyte RRs for urea, GSA, G, and MG (P < 0.01).
Limitations
Discrepancies were found between the biochemical and mathematical approaches. Hence, the erythrocyte compartment does not necessarily conform to the kinetic nonperfused compartment.
Conclusions
Our data indicate by means of direct estimations that the compartmental behaviors of guanidino compounds and urea are substantially different. Hence, we should consider that not all changes in concentrations in uremia and dialysis are representatively reflected by urea kinetics, even when considering other small water-soluble substances, such as the guanidino compounds.
1Institute for Biomedical Technology, Ghent University, Ghent, Belgium
2Laboratory of Neurochemistry and Behaviour, University of Antwerp, Antwerp, Belgium
3Nephrology Section, Ghent University Hospital, Ghent, Belgium.
Address correspondence to Sunny Eloot, PhD, MScBME, MScCivE, Institute for Biomedical Technology, Ghent University, De Pintelaan 185, Ghent, 9000 Belgium.
ABSTRACT