EFFECT OF AGE ON PROTEIN CATABOLIC RATE, MORBIDITY, AND MORTALITY IN UREMIC PATIENTS WITH ADEQUATE DIALYSIS

To test the validity of the assumption that the protein catabolic rate (PCRn g/kg/day) is dependent on the normalized dose of dialysis (Kt/V urea), and to try to define the characteristics of the patients in the undefined domain A of the mechanistic map of the National Cooperative Dialysis Study (NCDS), which should include patients with adequate amount of dialysis but inadequate PCRn, urea kinetic modelling was performed over 12 months on 85 patients undergoing haemodialysis. All the patients were managed to maintain a Kt/V urea greater-than-or-equal-to 0.9. During the entire period of study the total number of hospitalizations and the number of days of hospitalization were recorded. Total serum proteins and serum albumin concentrations were measured at the start and at the end of the study. The results of the study show that there was no correlation between Kt/V and PCRn nor between Kt/V and patient's age, but there was a strong inverse correlation between age and PCRn (r=0.578; P<0.0001). Further division of the patients into four groups according to age showed that the lowest values of PCRn were for the group of patients greater-than-or-equal-to 75 years old. Twelve patients with PCRn less-than-or-equal-to 0.8 and Kt/V greater-than-or-equal-to 0.9 were included in domain A of the mechanistic map. Eleven (92%) of these 12 patients were greater-than-or-equal-to 65 years old. No correlations were found between the total number of hospitalizations, the total days of hospitalization, Kt/V, time on HD, body weight and PCRn by multiple regression analysis, while the inverse correlation between PCRn and age was confirmed. Body weight, total serum proteins and serum albumin concentration remained stable throughout the study. However, the basal serum albumin was less in the group of patients greater-than-or-equal-to 75 years old. We conclude that if an adequate amount of dialysis is delivered, the protein intake becomes independent of the quantity of dialysis and dependent on other factors not yet known. In this situation, the age of the patients exerts a great negative influence on PCRn, particularly in patients greater-than-or-equal-to 75 years old. In the 12 patients from the whole group with Kt/V greater-than-or-equal-to 0.9 and PCRn less-than-or-equal-to 0.8 g/kg/day (domain A of the mechanistic map), we could find no differences in death, hospitalization rate, or duration of hospitalization compared to the others, The reduced PCRn in the oldest patients does not affect body weight, total serum protein, and serum albumin concentrations over time. This suggests that these patients might do well even with less protein intake.