Gender differences in normalized clearances in CAPD: role of body size and normalizing parameters.
OBJECTIVE
To compare raw (not normalized) and normalized urea and creatinine clearances between women and men on continuous ambulatory peritoneal dialysis (CAPD). To study whether potential gender differences are due to the normalization process.


METHODS
Retrospective analysis of clearance studies.


METHODS
Dialysis units of four academic medical centers.


METHODS
The study included 302 subjects (135 women and 167 men) on CAPD with four daily exchanges and a 2-L exchange volume.


METHODS
Measurement of urea and creatinine clearances (261 in women, 352 in men) by standard methods. Body water (the volume of distribution, V, for both urea and creatinine) was estimated by the Watson anthropometric formulas.


METHODS
Comparison of raw and normalized clearances between women and men. Urea clearance was normalized by V (Kt/Vur), while creatinine clearances was normalized by both V (Kt/Vcr) and body surface area (BSA) (Ccr).


RESULTS
Mean values of weekly total (peritoneal plus renal) raw clearances were higher in men (urea clearance: women 67.1 L, men 77.4 L; Ccr: women 61.7 L, men 78.3 L). Raw renal clearances were higher in men, while raw peritoneal clearances were comparable. Mean weekly total Kt/Vur was higher in women (2.19 vs 1.94 in men), mean weekly total Kt/Vcr did not differ between the genders (women 2.01, men 1.95), while mean weekly Ccr was higher in men (73.0 vs 64.7 L/1.73 m2 in women). When clearances differed, the differences were significant at p < 0.001. Men had greater height and weight, while women had greater body mass index. On the average, V in men exceeded V in women by 31%, while BSA in men exceeded BSA in women by only 12%.


CONCLUSIONS
Normalization of clearances by V creates relatively higher clearance values in women, while normalization by BSA creates relatively higher clearance values in men. Thus the normalization process may create artificial differences in the normalized clearances between genders.
Tzamaloukas
A H
AH
Veterans Affairs Medical Center and Department of Medicine, University of New Mexico School of Medicine, Albuquerque 87108, USA.
Murata
G H
GH
Bernardini
J
J
Malhotra
D
D
Rao
P
P
Piraino
B
B
Oreopoulos
D G
DG
D001824:Body Constitution; D001834:Body Water; D003404:Creatinine / Q000378:metabolism; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000378:metabolism / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010531:Peritoneal Dialysis, Continuous Ambulatory; D012737:Sex Factors; D014508:Urea / Q000378:metabolism
D014508:Urea; D003404:Creatinine