Urinary Urea Excretion and Long-term Outcome After Renal Transplantation.
BACKGROUND
Little is known about optimal protein intake after transplantation. The aim of this study was to prospectively investigate associations of urinary urea excretion, a marker for protein intake, with graft failure and mortality in renal transplant recipients (RTR) and potential effect modification by body mass index (BMI) and estimated glomerular filtration rate (eGFR).


METHODS
Urinary urea excretion was measured in repeated 24-hr urine collections between 6 and 18 months after transplantation.


RESULTS
In total, 940 RTR were included. During 4.4 (2.3-7.8) years of follow-up for graft failure and 4.8 (2.5-8.3) years for all-cause mortality, 78 RTR developed graft failure and 158 RTR died. Urinary urea excretion was not associated with graft failure in the overall population, but was inversely associated with graft failure in RTR with BMI less than 25 kg/m (hazard ratio [HR], 0.64 [0.28-1.50] and 0.27 [0.09-0.83] for the second and third tertiles, respectively, P < 0.001), and in RTR with eGFR of 45 mL per min per 1.73 m or higher (HR, 0.34 [0.15-0.79], P = 0.015 and HR, 0.31 [0.11-0.86], P = 0.025 for the second and third tertiles, respectively), both independent of potential confounders. Compared to the first tertile, RTR in the second and third tertiles of urinary urea excretion were at a lower risk of all-cause mortality (HR, 0.47 [0.32-0.69]; P < 0.001 and HR, 0.42 [0.26-0.68]; P < 0.001, respectively), independent of potential confounders. Body mass index and eGFR did not influence this association.


CONCLUSIONS
Urinary urea excretion, a marker for protein intake, was inversely related to graft failure in RTR with BMI less than 25 kg/m and in RTR with an eGFR of 45 mL per min per 1.73 m or higher. In addition, urinary urea excretion was inversely related to mortality.
1 Department of Medicine, University of Groningen, University Medical Center Groningen, the Netherlands. 2 Division of Human Nutrition, Wageningen University, the Netherlands. 3 Department of Laboratory Medicine, University Medical Center Groningen, the Netherlands. 4 Top Institute Food & Nutrition, Wageningen, the Netherlands.
Petronella E
PE
Deetman
M Yusof
MY
Said
Daan
D
Kromhout
Robin P F
RP
Dullaart
Jenny E
JE
Kootstra-Ros
Jan-Stephan F
JS
Sanders
Marc A J
MA
Seelen
Rijk O B
RO
Gans
Gerjan
G
Navis
Michel M
MM
Joosten
Stephan J L
SJ
Bakker
D000328:Adult; D015992:Body Mass Index; D003404:Creatinine / Q000652:urine; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D016030:Kidney Transplantation / Q000401:mortality; D008297:Male; D008875:Middle Aged; D014508:Urea / Q000652:urine*
D014508:Urea; D003404:Creatinine