Patients’ characteristics
As shown in Fig. 1, there were 180 patients (52.8% of male) participating in the study in total. Baseline characteristics of patients enrolled was detailedly presented in Table 1. The patients had a mean age of 45.0 ± 13.4 years old and a median dialysis vintage of 1.6(1.4–19.8) month. The leading primary kidney disease was chronic glomerulonephritis (67.2%), followed by diabetic nephropathy (8.9%), hypertensive lesions (7.8%) and others (16.1%). Mean SUA and peritoneal UA clearance was 6.9 ± 1.2 mg/dL and 40.2 ± 7.1 L/week/1.73 m2, respectively. At enrollment, there were 15.0% patients using diuretic during one month before the PET and Kt/V tests. The patients of higher peritoneal UA clearance were older, had a greater proportion of female and H transporters, smaller proportion of LA transporters, and had longer PD vintage, higher level of average glucose concentration of dialysate, peritoneal Kt/V, peritoneal CCL, corrected calcium and lower level of BMI, residual renal Kt/V, renal CCL, residual urine volume, serum albumin, and SUA.
Table 1
The characteristics of patients enrolled in the study.
Variables | Total (n = 180) | Lower peritoneal UA clearance (n = 90) | Higher peritoneal UA clearance (n = 90) | P value |
Peritoneal UA clearance(L/week/1.73 m2) | 40.2 ± 7.1 | 34.6 ± 3.5 | 45.8 ± 5.0 | -- |
Age (y) | 45.0 ± 13.4 | 42.9 ± 13.2 | 47.1 ± 13.3 | 0.04 |
Male (n, %) | 95(52.8) | 55(61.1) | 40(44.4) | 0.04 |
Diabetes (n, %) | 24(13.3) | 13(14.4) | 11(12.2) | 0.83 |
CVD (n, %) | 25(13.9) | 10(11.1) | 15(16.7) | 0.39 |
Charlson comorbidity score | 3(2–4) | 2(2–4) | 3(2–4) | 0.09 |
Chronic glomerulonephritis (n, %) | 121(67.2) | 63(70.0) | 58(64.4) | 0.53 |
Diabetic nephropathy (n, %) | 16(8.9) | 8(8.9) | 8(8.9) | 1.00 |
Hypertensive kidney lesion (n, %) | 14(7.8) | 5(5.6) | 9(10.0) | 0.41 |
PD vintage (m) | 1.6(1.4–19.8) | 1.5(1.3–8.4) | 2.3(1.4–49.9) | 0.01 |
Average dialysate glucose concentration (%) | 1.5(1.5–1.7) | 1.5(1.5–1.5) | 1.5(1.5–1.8) | < 0.001 |
DAPD (n, %) | 12(6.7) | 4(3.2) | 8(4.8) | 0.37 |
Total Kt/V | 2.3 ± 0.5 | 2.2 ± 0.4 | 2.4 ± 0.6 | 0.03 |
Residual renal Kt/V | 0.7 ± 0.5 | 0.8 ± 0.4 | 0.6 ± 0.5 | 0.02 |
Peritoneal Kt/V | 1.7 ± 0.3 | 1.5 ± 0.3 | 1.8 ± 0.3 | < 0.001 |
CCL (L/week/1.73 m2) | 76.1(60.4–93.1) | 76.8(63.2–94.7) | 74.7(59.0-91.5) | 0.36 |
Residual renal CCL (L/week/1.73 m2) | 30.4(10.4–49.8) | 38.3(20.4–56.1) | 22.5(1.5–44.0) | < 0.001 |
Peritoneal CCL (L/week/1.73 m2) | 46.1(41.0-51.3) | 41.3(38.7–43.2) | 50.9(48.0-56.6) | < 0.001 |
mGFR (mL/min/1.73 m2) | 3.1 ± 2.4 | 3.8 ± 2.4 | 2.3 ± 2.3 | < 0.001 |
Residual urine volume (L) | 0.700(0.300–1.200) | 0.850(0.550–1.225) | 0.555(0.050–1.100) | 0.003 |
nPCR (g/kg/d) | 0.889(0.769–1.076) | 0.856(0.765–1.028) | 0.934(0.785–1.126) | 0.05 |
PET category (%) |
High | 15(8.3) | 1(1.1) | 14(15.6) | 0.001 |
High average | 107(59.4) | 47(52.2) | 60(66.7) | 0.07 |
Low average | 54(30.0) | 38(42.2) | 16(17.8) | 0.001 |
Low | 4(2.2) | 4(4.4) | 0(0.0) | 0.13 |
Systolic pressure (mmHg) | 135.0 ± 18.0 | 134.6 ± 17.4 | 135.5 ± 18.7 | 0.73 |
Diastolic pressure (mmHg) | 85.5 ± 14.2 | 87.5 ± 12.7 | 83.5 ± 15.4 | 0.06 |
Hemoglobin (g/dL) | 11.2 ± 1.7 | 11.4 ± 1.6 | 11.0 ± 1.7 | 0.11 |
N/L | 3.5(2.7–4.5) | 3.2(2.6–4.2) | 3.7(2.9–4.8) | 0.11 |
HsCRP (mg/L) | 1.4(0.5–4.7) | 1.5(0.6–4.9) | 1.3(0.5–4.8) | 0.79 |
ALP (U/L) | 82.0(69.0-104.8) | 80.5(69.8-104.3) | 85.5(68.0-110.3) | 0.45 |
Serum albumin (g/dL) | 3.7 ± 0.4 | 3.8 ± 0.3 | 3.5 ± 0.4 | < 0.001 |
Serum prealbumin (mg/L) | 351(320–402) | 354(319–406) | 347(319–387) | 0.26 |
Corrected calcium (mg/dL) | 9.2 ± 1.0 | 9.1 ± 0.6 | 9.3 ± 1.2 | 0.22 |
Serum phosphorus (mg/dL) | 4.5 ± 1.3 | 4.5 ± 1.1 | 4.5 ± 1.5 | 0.93 |
Total cholesterol (mg/dL) | 193.4(162.4-228.2) | 193.4(158.5-230.1) | 193.4(166.3-228.2) | 0.62 |
Triglyceride (mg/dL) | 136.4(97.8-190.8) | 142.1(102.7-196.8) | 131.9(94.7-185.1) | 0.27 |
Serum urea nitrogen (mg/dL) | 45.5(37.5–55.7) | 45.4 (37.7–55.8) | 45.9(36.6–55.9) | 0.91 |
Serum creatinine (mg/dL) | 8.6(7.3–10.8) | 8.4(7.1–10.8) | 8.9(7.3–10.9) | 0.75 |
Serum UA (mg/dL) | 6.9 ± 1.2 | 7.2 ± 1.2 | 6.6 ± 1.2 | < 0.001 |
iPTH (pg/mL) | 256.2(149.4-401.4) | 256.2(164.0-391.1) | 258.0(139.6-454.3) | 0.82 |
BMI (kg/m2) | 21.8 ± 3.2 | 22.6 ± 3.2 | 21.0 ± 3.0 | 0.001 |
Diuretic use (n, %) | 27(15.0) | 11(12.2) | 16(17.8) | 0.40 |
Note: Values are presented as means ± standard deviation or median (interquartile range) for continuous variables and count (percentage) for categorical variables. |
Abbreviations: ALP, alkaline phosphatase; BMI, body mass index; CCL, weekly total creatinine clearance; CVD, cardiovascular disease; DAPD, Day Ambulatory Peritoneal Dialysis; HsCRP, high sensitivity C-reactive protein; iPTH, intact parathyroid hormone; mGFR, measured glomerular filtration rate; N/L, neutrophil to lymphocyte ratio; nPCR, normalized protein catabolic rate; PD, peritoneal dialysis; PET, peritoneal equilibration test; UA, uric acid;. |
Peritoneal UA removal and its relationship with SUA in PD patients
The distribution of SUA in PD patients was shown in Fig. 2a. The average mass transfer of urea, creatinine or UA with 2L of 2.5% dextrose dialysate for a dwell time of 0 or 4 hours of all PD patients were described in detail in Fig. 2b. Similar to the small molecular of urea and creatinine, the peritoneal mass transfer of UA was remarkably declined with the lengthening of dwell time. Different from the positive correlation between average UA mass transfer for 4 hours’ dwell and SUA (r = 0.55, P < 0.001), the peritoneal UA clearance was found to be inversely correlated to the SUA (r=-0.25, P = 0.001) level (Fig. 2c and 2d). In comparison to normal SUA group, the hyperuricemia group showed significantly lower peritoneal UA clearance (39.1 ± 6.2 vs. 42.0 ± 8.0 L/week/1.73 m2, P = 0.008). The further analysis of multiple linear regression (β -0.21, 95%CI -0.07, -0.006, P = 0.02) and binary logistic regression (OR 0.91, 95%CI 0.84, 0.98, P = 0.02) shown in Table 2 and Table 3 both revealed that it was not the residual kidney function of mGFR but the peritoneal UA clearance that was independently associated with SUA in PD patients.
Table 2
Associated factors of SUA in multiple linear regression.
Variables | β (95%CI) | P value |
Age (y) | -0.17 (-0.03, -0.001) | 0.04 |
Sex (M/F) | 0.08 (-0.15, 0.54) | 0.27 |
Diabetes | -0.05 (-0.70,0.33) | 0.48 |
CVD | -0.08 (-0.81,0.25) | 0.30 |
Using diuretics | -0.12 (-0.54, 0.40) | 0.78 |
PD vintage (m) | -0.08 (-0.01, 0.004) | 0.39 |
Mean arterial pressure (mmHg) | -0.02 (-0.01,0.01) | 0.80 |
BMI (kg/m2) | 0.28 (0.05, 0.17) | < 0.001 |
Albumin (g/dL) | -0.05 (-0.62, 0.31) | 0.51 |
nPCR (g/kg/d) | 0.38 (1.11, 2.79) | < 0.001 |
mGFR (mL/min/1.73 m2) | -0.09 (-0.13, 0.04) | 0.32 |
Peritoneal UA clearance (L/week/1.73 m2) | -0.21 (-0.07, -0.006) | 0.02 |
Abbreviations: BMI, body mass index; CI, confidence interval; CVD, cardiovascular disease; mGFR, measured glomerular filtration rate; nPCR, normalized protein catabolic rate; PD, peritoneal dialysis; SUA, serum uric acid; UA, uric acid. |
Table 3
Independent determinants of higher SUA in binary logistic regression.
Variables | Adjusted OR (95%CI) | P value |
Age (y) | 0.95 (0.92, 0.99) | 0.005 |
Sex (M/F) | 0.12 (-0.15, 0.54) | < 0.001 |
Diabetes | 0.90 (0.29,2.74) | 0.85 |
CVD | 1.30 (0.38,4.44) | 0.68 |
Using diuretics | 0.94 (0.34, 2.60) | 0.90 |
PD vintage (m) | 1.00 (0.99, 1.02) | 1.00 |
Mean arterial pressure (mmHg) | 1.01 (0.98,1.04) | 0.39 |
BMI (kg/m2) | 1.09 (0.95, 1.25) | 0.21 |
Albumin (g/dL) | 0.91 (0.32, 2.64) | 0.86 |
nPCR (every 0.1 g/kg/d) | 1.39 (1.12, 1.73) | 0.003 |
mGFR (mL/min/1.73 m2) | 0.99 (0.82,1.19) | 0.88 |
Peritoneal UA clearance (L/week/1.73 m2) | 0.91 (0.84, 0.98) | 0.02 |
Abbreviations: BMI, body mass index; CI, confidence interval; CVD, cardiovascular disease; mGFR, measured glomerular filtration rate; nPCR, normalized protein catabolic rate; OR, odds ratio; PD, peritoneal dialysis; SUA, serum uric acid; UA, uric acid. |
The relationship between peritoneal UA clearance and peritoneal transport characteristics
The distribution of the peritoneal UA clearance in different peritoneal transport characteristics was shown in Fig. 3a, which indicated a progressively increase of peritoneal UA clearance with the elevating of the peritoneal transport rate. It was revealed that the higher (H or HA) transporters possessed significantly higher peritoneal UA clearance than the lower (LA or L) transporters (42.0 ± 7.0 vs. 36.4 ± 5.6 L/week/1.73 m2, P < 0.001). Besides, as shown in Fig. 3b, the 4 h dialysate to plasm (D/P) UA was highly correlated with the 4 h D/P creatinine (r = 0.97, P < 0.001). And the correlation between the 4 h D/P UA and peritoneal UA clearance (r = 0.47, P < 0.001) and between the 4 h D/P creatinine and peritoneal UA clearance (r = 0.46, P < 0.001) were similar (Fig. 3c and Fig. 3d).
Independent influencing factors of peritoneal UA clearance
As shown in Table 4, after adjusting the common variables such as age, sex, dialysis vintage, mGFR, BMI and the history of using diuretics in multiple linear regression model, the serum albumin level was found to be negatively associated with peritoneal UA clearance (β -0.06, 95%CI -2.09, -0.19, P = 0.02), while the higher transporters (β 0.06, 95%CI 0.05, 1.69, P = 0.04) and peritoneal CCL (β 0.95, 95%CI 0.81, 0.93, P < 0.001) were positively associated with peritoneal UA clearance. Similarly, the further binary logistic regression analysis (shown in Table 5) revealed that every 1L/week/1.73 m2 increase of the peritoneal CCL (OR 1.95, 95%CI 1.53,2.50, P < 0.001) or every 1 g/dL decrease of albumin level (OR 0.15, 95%CI 0.05,0.47, P = 0.001) were independently associated with greater peritoneal UA clearance (> 39.8 L/week/1.73 m2). Furthermore, the peritoneal CCL was found to perform best in ROC analysis (AUC = 0.96, 95%CI 0.93–0.99, P < 0.001) to predict higher peritoneal UA clearance among the widely used small solute removal indicators (shown in Fig. 4).
Table 4
Associated factors of peritoneal UA clearance in multiple linear regression.
Variables | β (95%CI) | P value |
Age (y) | 0.02 (-0.02, 0.04) | 0.49 |
Sex (M/F) | 0.02 (-0.48, 0.92) | 0.53 |
Using diuretics | 0.003 (-0.90, 1.03) | 0.90 |
Albumin (g/dL) | -0.06 (-2.09, -0.19) | 0.02 |
PD vintage (month) | -0.05 (-0.02, 0.004) | 0.16 |
Average glucose concentration of dialysate (0.1%) | 0.01 (-0.14, 0.22) | 0.64 |
BMI (kg/m2) | -0.002 (-0.12, 0.11) | 0.95 |
nPCR (g/kg/d) | 0.007 (-1.46, 1.79) | 0.80 |
mGFR (mL/min/1.73 m2) | 0.06 (-0.02, 0.34) | 0.07 |
Higher peritoneal transport status a | 0.06 (0.05, 1.69) | 0.04 |
Peritoneal CCL (L/week/1.73 m2) | 0.95 (0.81, 0.93) | < 0.001 |
a The reference group was the lower (low average or low) peritoneal transporters. |
Abbreviations: BMI, body mass index; CCL, weekly total creatinine clearance; CI, confidence interval; mGFR, measured glomerular filtration rate; nPCR, normalized protein catabolic rate; PD, peritoneal dialysis; UA, uric acid. |
Table 5
Independent determinants of higher peritoneal UA clearance in binary logistic regression.
Variables | Adjusted OR (95%CI) | P value |
Age (y) | 1.01 (0.96, 1.06) | 0.61 |
Sex (M/F) | 0.46 (0.13, 1.60) | 0.22 |
Using diuretics | 0.68 (0.13, 3.48) | 0.64 |
Albumin (g/dL) | 0.15 (0.05, 0.47) | 0.001 |
PD vintage (month) | 0.98 (0.95, 1.02) | 0.35 |
Average glucose concentration of dialysate (0.1%) | 1.27 (0.85, 1.90) | 0.24 |
BMI (kg/m2) | 1.02 (0.82, 1.27) | 0.85 |
nPCR (g/kg/d) | 0.52 (0.04, 6.54) | 0.61 |
mGFR (mL/min/1.73 m2) | 1.31 (0.92, 1.87) | 0.32 |
Higher peritoneal transport status a | 1.61 (0.40, 6.44) | 0.50 |
Peritoneal CCL (L/week/1.73 m2) | 1.95 (1.53, 2.50) | < 0.001 |
a The reference group was the lower (low average or low) peritoneal transporters. |
Abbreviations: BMI, body mass index; CCL, weekly total creatinine clearance; CI, confidence interval; mGFR, measured glomerular filtration rate; nPCR, normalized protein catabolic rate; PD, peritoneal dialysis; UA, uric acid. |