Reproducibility of serial creatinine excretion measurements in peritoneal dialysis

AIM: To test whether muscle mass evaluated by creatinine excretion (EX(Cr)) is maintained in patients with end-stage kidney disease (ESKD) treated by peritoneal dialysis (PD), we evaluated repeated measurements of EX(Cr) in a PD population. METHODS: One hundred and sixty-six PD patients (94 male, 72 female) receiving the same PD dose for the duration of the study (up to approximately 2.5 years) had repeated determinations of total (in urine plus spent dialysate) 24-h EX(Cr) (EX(Cr) T) to assess the adequacy of PD by creatinine clearance. All 166 patients had two EX(Cr) T determinations, 84 of the 166 patients had three EX(Cr) T determinations and 44 of the 166 patients had four EX(Cr) T measurements. EX(Cr) T values were compared using the paired t test in the patients who had two studies and by repeated measures ANOVA in those who were studied three or four times. RESULTS: In patients who were studied twice, with the first and second EX(Cr) T measurements performed at 9.2 ± 15.2 mo and 17.4 ± 15.8 mo after onset of PD, respectively, EX(Cr) T did not differ between the first and second study. In patients studied three times and whose final assessment occurred 24.7 ± 16.3 mo after initiating PD, EX(Cr) T did not differ between the first and second study, but was significantly lower in the third study compared to the first study. In patients who were studied four times and whose fourth measurement was taken 31.9 ± 16.8 mo after onset of PD, EX(Cr) T did not differ between any of the studies. The average EX(Cr) T value did not change significantly, with the exception of the third study in the patients studied thrice. However, repeated determinations of EX(Cr) T in individuals showed substantial variability, with approximately 50% of the repeated determinations being higher or lower than the first determination by 15% or more. CONCLUSION: The average value of EX(Cr) T remains relatively constant for up to 2.5 years of follow-up in PD patients who adhere to the same PD schedule. However, repeated individual EX(Cr) T values vary considerably in a large proportion of the patients. Further studies are needed to evaluate the clinical significance of varying EX(Cr) T values and the stability of EX(Cr) T beyond 2.5 years of PD follow-up.