The diagnostic accuracy of urinary neutrophil gelatinase-associated lipocalin in assessing kidney function in severe hydronephrosis

Abstract

Background: Up to now, there is no perfect indicator to evaluate the renal function of severe hydronephrosis, which poses difficulties in the selection of clinical treatment decisions. This study investigates the role of neutrophil gelatinase-associated lipocalin (NGAL) in urine drained from the nephrostomy tube shortly after nephrostomy to evaluate the renal function of patients with severe hydronephrosis caused by ureteral obstruction.

Methods: The clinical data, and blood and urine samples of 24 patients with severe hydronephrosis due to ureteral obstruction were retrospectively collected. The NGAL in the urine drained from the nephrostomy tube on the morning of the first day after the procedure was measured. The glomerular filtration rate (GFR) was determined using a nuclear scan, and the clearance rate of creatinine was calculated based on nephrostomy drainage. The correlation between the NGAL level, urine volume post-nephrostomy, affected side GFR, and creatinine clearance rate (Ccr) was assessed. Moreover, the relationship between the urinary NGAL levels and prognosis was analyzed based on whether the patients underwent nephrectomy.

Results: There was a significant correlation between the urine NGAL from the nephrostomy of the affected side and the Ccr and urine volume post-nephrostomy (both P<0.05). Compared with the patients in the kidney preservation group, those who underwent nephrectomy had significantly increased NGAL levels, and significantly reduced Ccrs and nephrostomy drainage urine output. Through the receiver operating characteristic (ROC) curve evaluation, the efficacy of NGAL in predicting nephrectomy was found to be superior to both the Ccr and urine output, with an area under the curve (AUC) of 0.845.

Conclusions: The NGAL in the urine shortly after nephrostomy may indicate severe renal functional deterioration.

Keywords: Hydronephrosis; creatinine clearance rate (Ccr); glomerular filtration rate (GFR); neutrophil gelatinase-associated lipocalin (NGAL); renal function.

Figure 1

Study flow chart for patients. CT, computed tomography.

Figure 2

Correlation between NGAL and patients’ clinical data. (A) Correlation between NGAL and POST1; (B) correlation between NGAL and POST2; (C) correlation between NGAL and POST3; (D) correlation between NGAL and GFR of the affected side; (E) correlation between NGAL and Ccr of the affected side. “POST1” represents the urine volume during the first day after nephrectomy from the nephrostomy tube; “POST2” represents the urine volume during the second day after nephrectomy from the nephrostomy tube; “POST3” represents the urine volume during the third day after nephrectomy from the nephrostomy tube. NGAL, neutrophil gelatinase-associated lipocalin; GFR, glomerular filtration rate; Ccr, creatinine clearance rate.

Figure 3

Comparison of the clinical data (NGAL level, the Ccr, the GFR of the affected side, and the first three urine volumes) between patients in the nephrectomy and non-nephrectomy groups. The control group refers to the non-nephrectomy group. The surgery group refers to the nephrectomy group. (A) Comparison of the NGAL level between patients in the nephrectomy and non-nephrectomy groups; (B) comparison of the Ccr between patients in the nephrectomy and non-nephrectomy groups; (C) comparison of the GFR of the affected side between patients in the nephrectomy and non-nephrectomy groups; (D) comparison of the POST1 between patients in the nephrectomy and non-nephrectomy groups; (E) comparison of the POST2 between patients in the nephrectomy and non-nephrectomy groups; (F) comparison of the POST3 between patients in the nephrectomy and non-nephrectomy groups. “POST1” represents the urine volume during the first day after nephrectomy from the nephrostomy tube; “POST2” represents the urine volume during the second day after nephrectomy from the nephrostomy tube; and “POST3” represents the urine volume during the third day after nephrectomy from the nephrostomy tube. NGAL, neutrophil gelatinase-associated lipocalin; Ccr, creatinine clearance rate; GFR, glomerular filtration rate.

Figure 4

ROC curves showing the ability of NGAL, the urine volume, and the Ccr to predict nephrectomy in patients with severe hydronephrosis. (A) ROC curves showing the ability of NGAL to predict nephrectomy in patients with severe hydronephrosis. (B) ROC curves showing the ability of urine volume from the nephrostomy tube on the third day post-nephrectomy to predict nephrectomy in patients with severe hydronephrosis. (C) ROC curves showing the ability of the Ccr to predict nephrectomy in patients with severe hydronephrosis. (D) Combination prediction model of NGAL, the urine volume, and the Ccr. Sens, sensitivity; Spec, specificity; PPV, positive predictive value; NPV, negative predictive value; AUC, area under the curve; ROC, receiver operating characteristic; NGAL, neutrophil gelatinase-associated lipocalin; Ccr, creatinine clearance rate.