Change over time in Pre-ESRD 24-hour urine creatinine as muscle mass surrogate and post-ESRD mortality.

OBJECTIVE: Loss of muscle mass and sarcopenia are common in CKD and ESRD, and sarcopenia can worsen insidiously in patients with advancing CKD. The temporal dynamics of sarcopenia in patients with progressive loss of kidney function, and its association with future outcomes, is unclear.

METHODS: In a contemporary national cohort of incident ESRD US veterans, we selected 661 patients who had at least two 24-hour urine creatinine (24hrUC) measurements, a surrogate of muscle mass, performed during the 3-year prelude period prior to ESRD transition. We estimated 24hrUC slopes in mixed effects models. To assess the temporal dynamics of pre-ESRD changes in 24hrUC and its association with changing eGFR, we separately fitted in mixed effects models a penalized spline regression of 24hrUC on time and on eGFR. We examined the association of 24hrUC slopes with post-dialysis all-cause mortality using Cox models adjusted for confounders.

RESULTS: The mean slope of 24hrUC vs. time was -78 mg/year (95%CI: -102 to -54), with a steeper decline noted in the last year prior to ESRD. More severe decreases in 24hrUC were associated with higher all-cause mortality: a 100 mg/year decrease in 24hrUC was associated with a multivariable adjusted death hazard ratio of 1.41 (95%CI: 1.00-1.98, p=0.05).

CONCLUSION: Patients with advanced CKD lose a substantial proportion of their muscle mass each year during pre-ESRD prelude. Loss of muscle mass accelerates near ESRD transition, and more loss of muscle mass is associated with higher mortality after ESRD transition.