Sodium removal and sodium concentration during peritoneal dialysis: effects of three methods of sodium measurement.
BACKGROUND
Sodium removal (NaR) may have a major impact on the survival of peritoneal dialysis patients. The dialysate/plasma sodium concentration ratio (D/P(Na)) is an indirect index of transcellular water transport by aquaporin channels, and thus of ultrafiltration. Sodium concentration can be assessed by means of flame photometry (F), and direct (D-ISE) or indirect ion-selective electrodes (I-ISE), but these methods have different properties. I-ISE is being used increasingly in clinical laboratories. The aim of this study was to evaluate NaR and D/P(Na) using the three different measurement methods.


METHODS
We performed peritoneal equilibration tests (PETs) in 44 peritoneal dialysis patients and calculated the NaR. We also calculated D/P(Na) during the test; plasma and dialysate sodium concentrations were measured by F, D-ISE and I-ISE.


RESULTS
NaR was lower (P<0.001) with D-ISE (69+/-29 mmol) than with F (81+/-29 mmol) or I-ISE (79+/-28 mmol). D/P(Na) was also lower at baseline (0.92+/-0.02 vs 0.95+/-0.02 and 0.95+/-0.02; P<0.001), after 60 min (0.87+/-0.03 vs 0.90+/-0.03 and 0.90+/-0.03; P<0.001) and at the end of PET (0.88+/-0.04 vs 0.92+/-0.04 and 0.92+/-0.04; P<0.001) when measured by D-ISE in comparison with F and I-ISE, respectively.


CONCLUSIONS
NaR and D/P(Na) were lower when measured by the D-ISE method compared with the F and I-ISE methods. NaR and D/P(Na) were similar when measured by F or I-ISE. I-ISE can be used reliably in the evaluation of NaR and D/P(Na) in everyday clinical practice of peritoneal dialysis.
La Milia
Vincenzo
V
Department of Nephrology and Dialysis, A Manzoni Hospital, Lecco, Italy. v.lamilia@ospedale.lecco.it
Di Filippo
Salvatore
S
Crepaldi
Monica
M
Andrulli
Simeone
S
Del Vecchio
Lucia
L
Scaravilli
Pietro
P
Virga
Giovambattista
G
Locatelli
Francesco
F
D019963:Clinical Chemistry Tests / Q000379:methods; D005260:Female; D017583:Hemodiafiltration / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D010530:Peritoneal Dialysis; D012964:Sodium / Q000032:analysis / Q000378:metabolism*
D012964:Sodium