Since the urea kinetic model is used as an objective method for monito
ring dialysis, it has been possible to shorten reasonably its duration
. From the usual practice, we have observed that it is easier to reduc
e the dialysis time in women as compared to men. The purpose of this s
tudy is to find out the reason for such observation and to corroborate
it. Fourty-two patients, 25 males and 17 females on 3-weekly dialysis
(3 h/session) were studied. All patients were dialyzed under the same
dialysis characteristics: 3-hour sessions, blood flow 350 ml/min, ult
rafiltration 1.5 liters/h, 1.5-m(2) cuprophane membrane and bicarbonat
e buffer. The dialysate was collected in a graduated tank. Urea concen
tration in plasma and in the dialysate was measured. Then, the urea di
stribution volume, dialyzer clearance, the KT/Vindex and protein catab
olic rate were calculated. The KT/V value was higher in women with res
pect to men, 1,017 +/- 0.10 versus 0.82 +/- 0.14 (p < 0.001). The urea
distribution volume value was significantly higher in men as compared
to women, 60.04 +/- 6.6 versus 51.48 +/- 5.88% (p < 0.001). There wer
e no significant differences in dialyzer clearance, protein catabolic
rate or body weight. In conclusion, under identical dialysis condition
s, it is easier to dialyze women than men, because women's urea distri
bution volume is lower than men's.