Therapeutic Research

Abstract

Background：Patients with non‒dialysis chronic kidney disease（CKD）are widely instructed to have a protein‒restricted diet to inhibit progression of renal failure. However, patients with CKD are aging, and malnutrition is associated with poor prognosis. We retrospectively examined the association between mortality or renal prognosis in elderly patients with non‒dialysis CKD and the amount of protein intake, calculated using a 24‒hour cold storage pooled urine test. Methods：Of the 768 patients with CKD who visited Daiko Sunadabashi Clinic between September 2005 and August 2017, we included patients in whom cold storage 24‒hour pooled urine tests were performed at least once. The patients were divided into two groups―those with high and low normalized protein catabolic ratios（nPCRs）―and the outcomes and hazard ratios（HRs）were compared between the groups. The patients were also divided into groups based on age（65 and older or younger than 65 years）. The primary endpoint was mortality. The secondary endpoint was the induction of renal replacement therapy （RRT）. The baseline characteristics were tested using Student’s t‒test or a χ2 test. Survival was represented graphically using the Kaplan‒Meier method and analyzed using uni‒ and multivariate Cox regression analyses. Results：We assessed 233 men and 173 women with the age over 65. The mean age was 76.4±6.9 years. The mean creatinine clearance level was 48.0±36.3 mL/min/1.73 m2 and the mean nPCR was 0.888±0.285 g/day/kg. After adjustment, the nPCR was associated with mortality（HR：0.1849, 95％ confidence interval［CI］：0.0377‒0.9073, p＝0.0375）. The higher the nPCR, the higher the rate of RRT induction, but it was not significant（HR：2.3190, 95％ CI：0.8175‒6.5786, p＝0.1138）. An nPCR of 0.87051 was chosen as the cutoff value for the receiver operating characteristic curve to predict death. In patients under 65 years old, the rate of RRT induction tended to increase as the nPCR increased, but it was not significant. The nPCR value was unrelated to mortality. Conclusion：Restricting protein intake may be useful for suppressing progression of renal failure, but caution is necessary because restricting protein intake too severely in older people may be associated with deteriorated prognosis.