Detection values of urinary etinol binding protein in diagnosing hydronephrosis caused by ureteropelvic junction obstruction and optimizing truncation value for predicting renal damage

Abstract

Objective To explore the detection values of urinary retinol binding protein (RBP), albumin (ALB) and aquaporin-2 (AQP2) in children with hydronephrosis caused by ureteropelvic junction obstruction (UPJO) and predict the optimal cut-off value of renal damage. Methods A total of 89 hydronephrotic children undergoing surgery from March 2014 to September 2016 were collected.All children had hydronephrosis caused by unilateral UPJO.Among them, there were 62 boys and 27 girls with an average age of (1.14±0.47) (3 months to 2 years) years.Another 30 healthy children with normal renal function in the same period were selected as normal control group.There were 18 boys and 12 girls with an average age of (2.10±0.52)(1-3) years.All subjects were examined preoperatively by ultrasonography.According to thickness of renal parenchyma and degree of separation of set system, they were divided into group A (mild, n=20), group B (moderate, n=31) and group C (severe, n=38). The ultrasonic parameters (renal parenchymal thickness, renal volume & separation degree of renal collection system) and urinary levels of RBP, ALB and AQP2 were compared among four groups.The pathological grades of diseased kidney were resected in 89 cases after operation who were divided into hydronephrosis group, kidney damage group (pathological grade Ⅱ-Ⅴ) and no kidney damage group (pathological grade Ⅰ). Ultrasonic parameters and urinary levels of RBP, ALB and AQP2 were compared between two groups.The receiver operating characteristic (ROC) curves of RBP, ALB and AQP2 were plotted for predicting hydronephrosis and renal damage in three patients. Results No significant difference existed in renal parenchymal thickness or kidney volume between group A and normal control group (P>0.05) and separation degree of renal aggregation system was higher than that of normal control group (P<0.05). Renal parenchymal thickness showed a declining trend in groups A, B and C while renal volume and degree of separation of renal system showed an incremental trend (P<0.05). In normal control group, group A, group B and group C, RBP and ALB showed an upward trend while AQP2 had a downward trend (P<0.05). Linear correlation showed that RBP and ALB were negatively correlated with thickness of renal parenchyma (r=-0.453, -0.489, P<0.05) and AQP2 was positively correlated with thickness of renal parenchyma (r=0.327, P<0.05). RBP and ALB were positively correlated with volume of kidney and degree of separation of renal aggregate system (r=0.404, 0.375, 0.416, 0.402, P<0.05). AQP2 was negatively correlated with volume of kidney and separation degree of renal aggregate system (r=-0.331, -0.398, P<0.05). In hydronephrosis group, RBP and ALB were higher in renal damage group than those in hydronephrosis group while AQP2 was lower in hydronephrosis group than that in hydronephrosis group (P<0.05). The levels of RBP, ALB and urinary AQP2 all had predictive values for hydronephrotic kidney damage (P<0.05). The area under the ROC curve were 0.814, 0.815, 0.833 and the optimal cut-off values of diagnosing renal damage 214.00, 12.75, 55.10 respectively. Conclusions The levels of urine RBP, ALB and AQP2 are correlated with the degree of hydronephrosis, and all three had a certain predictive value for renal hydronephrosis. Key words: Hydronephrosis; Retinol-binding protein; Albumin; Aquaporin