Reproducibility of serial creatinine excretion measurements in peritoneal dialysis

Table 1 Patient characteristics n (%)

	Two clearance studies	Three clearance studies	Four clearance studies
Patient number	166	84	44
Age at onset of peritoneal dialysis, yr	52 ± 15	51 ± 16	51 ± 18
Male	94 (56.6)	46 (54.8)	26 (59.1)
Female	72 (43.4)	38 (45.2)	18 (40.9)
Diabetic nephropathy	73 (44.0)	36 (42.9)	17 (38.6)

Table 2 Creatinine excretion in patients with two studies

Variable	1st clearance study	2nd clearance study	P value
PD duration, mo	9.2 ± 15.2	17.4 ± 15.8
VU, L/24-h	0.54 ± 0.63	0.40 ± 0.53	< 0.001
VD, L/24-h	11.3 ± 3.2	12.1 ± 3.6	NS
Kt/V urea, weekly	2.30 ± 0.62	2.12 ± 0.03	0.003
CCr, L/1.73 m2, weekly	77.9 ± 32.1	67.9 ± 18.2	0.002
SUN, mg/dL	49.7 ± 15.1	49.4 ± 16.2	NS
[Cr]S, mg/dL	9.1 ± 3.3	10.1 ± 3.4	0.001
EXCr U, mg/24-h	406 ± 337	286 ± 350	0.003
EXCr D, mg/24-h	680 ± 337	769 ± 390	< 0.001
EXCr T, mg/24-h	1087 ± 470	1055 ± 421	NS

PD: Peritoneal dialysis; NS: Not significant; VU: Urine volume; VD: Drained volume of spent dialysate; Kt/V urea: Fractional urea clearance, weekly; C_Cr: Weekly renal plus peritoneal creatinine clearance; SUN: Serum urea nitrogen; [Cr]_S: Serum creatinine concentration; EX_Cr D: Creatinine excretion in spent dialysate; EX_Cr U: Creatinine excretion in urine; EX_Cr T: Total creatinine excretion in urine plus dialysate.

Table 3 Creatinine excretion in patients with three studies

Variable	1st clearance study	2nd clearance study	3rd clearance study	P value
PD duration, mo	8.6 ± 7.8	16.8 ± 11.6	24.7 ± 16.3
VU, L/24-h	0.58 ± 0.66	0.45 ± 0.59	0.38 ± 0.50	0.0001
VD, L/24-h	11.5 ± 4.0	11.8 ± 3.7	12.4 ± 3.7	NS
Kt/V urea, weekly	2.28 ± 0.65	2.14 ± 0.58	2.12 ± 0.63	0.0245
CCr, L/1.73 m2, weekly	79.3 ± 35.6	71.4 ± 27.8	68.0 ± 26.9	0.0335
SUN, mg/dL	50.4 ± 18.5	49.5 ± 17.9	49.2 ± 19.2	NS
[Cr]S, mg/dL	9.5 ± 3.5	9.8 ± 3.4	10.1 ± 3.3	0.0066
EXCr U, mg/24-h	418 ± 404	370 ± 425	286 ± 362	< 0.0001
EXCr D, mg/24-h	731 ± 379	767 ± 396	779 ± 382	NS1
EXCr T, mg/24-h	1149 ± 416	1137 ± 454	1065 ± 442	0.0087

¹Statistical trend (P = 0.0895). PD: Peritoneal dialysis; NS: Not significant; VU: Urine volume; VD: Drained volume of spent dialysate; Kt/V urea: Fractional urea clearance, weekly; C_Cr: Weekly renal plus peritoneal creatinine clearance; SUN: Serum urea nitrogen; [Cr]_S: Serum creatinine concentration; EX_Cr D: Creatinine excretion in spent dialysate; EX_Cr U: Creatinine excretion in urine; EX_Cr T: Total creatinine excretion in urine plus dialysate.

Table 4 Creatinine excretion in patients with four clearance studies

Variable	1st clearance study	2nd clearance study	3rd clearance study	4th clearance study	P value
PD duration, mo	8.1 ± 12.6	16.5 ± 4.4	24.5 ± 16.3	31.9 ± 16.8
VU, L/24-h	0.54 ± 0.55	0.41 ± 0.49	0.33 ± 0.40	0.29 ± 0.42	< 0.0001
VD, L/24-h	11.8 ± 3.9	12.2 ± 3.6	12.2 ± 3.5	12.5 ± 3.2	NS
Kt/V urea, weekly	2.27 ± 0.65	2.15 ± 0.56	2.13 ± 0.54	2.10 ± 0.55	0.0356
CCr, L/1.73 m2, weekly	77.5 ± 29.7	70.4 ± 28.5	68.5 ± 25.7	66.1 ± 22.1	0.0238
SUN, mg/dL	49.8 ± 16.7	49.5 ± 15.4	49.2 ± 15.3	49.0 ± 13.5	NS
[Cr]S, mg/dL	9.8 ± 3.6	10.2 ± 3.7	10.8 ± 3.8	10.8 ± 3.6	0.0009
EXCr U, mg/24-h	411 ± 438	382 ± 460	272 ± 345	282 ± 481	0.0011
EXCr D, mg/24-h	755 ± 406	788 ± 424	808 ± 438	853 ± 398	0.0021
EXCr T, mg/24-h	1166 ± 440	1170 ± 495	1080 ± 455	1135 ± 521	NS

PD: Peritoneal dialysis; NS: Not significant; VU: Urine volume; VD: Drained volume of spent dialysate; Kt/V urea: Fractional urea clearance, weekly; C_Cr: Weekly renal plus peritoneal creatinine clearance; SUN: Serum urea nitrogen; [Cr]_S: Serum creatinine concentration; EX_Cr D: Creatinine excretion in spent dialysate; EX_Cr U: Creatinine excretion in urine; EX_Cr T: Total creatinine excretion in urine plus dialysate.

Table 5 Number (percent) of studies with creatinine excretion deviating from baseline by < 15% and ≥ 15%

Study	< 15% from the 1st study	≥ 15% above the 1st study	≥ 15% below the 1st study
Second	90 (54.2%)	41 (24.7%)	35 (21.1%)
Third	40 (47.6%)	28 (33.3%)	16 (19.1%)
Fourth	24 (54.5%)	11 (25.0%)	9 (20.5%)