Obstructive uropathy (OU) is defined as an alteration at any level of the urinary tract that is caused by abnormalities in its system organs or external pathological factors. ¹ OU is a potentially life-threatening condition that can cause sepsis and/or acute kidney injury (AKI) and necessitates emergency decompression via retrograde ureteric stent placement, or a percutaneous insertion of a nephrostomy tube into the obstructed pelvicalyceal system. ^{2 , 3} The obstruction of the upper urinary tract, the development of hydronephrosis, and hydroureter may occur over a shorter time than the obstruction of the anatomically more distal, lower urinary tract. In OU cases secondary to lower urinary tract obstruction, adequate bladder drainage is the ultimate therapeutic goal, which can be achieved using urethral catheterization, or percutaneous cystostomy.

Despite adequate urinary drainage, improvement in renal function is not always achievable in OU cases. This could be related to other diseased processes affecting kidney function in addition to OU, and the length of urinary tract obstruction, which is often unknown, particularly in silent ureteral stone disease or cancer. ^{4 – 6} Several factors have been proposed in the literature, which may contribute to predicting whether improvement in renal function is expected after urinary diversion. The urgent decompression of the urinary tract would release the heightened urinary tract system pressure, also relieving the patient’s complaints. In the obstruction of the urinary tract, the therapeutic goal of urinary drainage is to adequately drain the upper urinary tracts for symptomatic relief while maintaining renal function, allowing systemic therapy to be initiated while minimizing urologic intervention, hospitalization, and negative impact on quality of life. In addition, urine diversion methods, especially the use of percutaneous nephrostomy, frequently have a detrimental influence on the patients' quality of life, limiting their mobility, the need for analgetic, urinary discomfort, hematuria, and personal hygiene. ⁴ Although these reasons should not prevent urinary diversion from being performed, clinically, it would be helpful to have clinical evidence of how significant and clinically beneficial urinary diversion is toward OU patients.

Because OU treatment carries the risk of complications, and urine diversion may affect the patient's quality of life, it should be thoroughly discussed with the patient and their family, particularly the prognosis. As a result, it's crucial to understand the factors that can predict renal function recovery after OU treatment.

The study of the predictive factor for successful urinary diversion using either nephrostomy or double J stent has been widely studied internationally. There are a variety of perioperative factors for predicting renal function recovery that vary from study to study. However, the study of predictive factor was still limited in the Indonesian population. This study aimed to analyze renal function recovery in the Indonesian population and health settings.

We collected 567 data from patients with OU whom received treatment with either nephrostomy or double J stent insertion. The baseline characteristic of each patient are included in Table 1. The laboratory parameters result are shown in Table 2.

Of 567 subjects, 358 had a successful operation, and the other 209 subjects had unimproved renal function parameters and categorized as failed subjects. For renal parenchymal thickness, 351 subjects had a good renal parenchymal thickness and 216 with poor thickness ( Table 3). We measured several laboratory parameters including haemoglobin (median value 11.60), haematocrit (median value 34.70), leucocyte (median value 9.170), thrombocyte (median value 337.000), blood urea (median value 38.00), creatinine serum (median value 1.58) and electrolytes (including natrium, with median value of 136; kalium, with a median value of 4,10 and chloride with a median value of 100.30).

We analysed the relation between parenchymal thickness with successfulness of the operation using Chi-Square. We found a statistically significant relationship (p-value < 0.01), with an estimated OR of 11.24 (p-value < 0.01, 95% CI 7.5 – 16.8). Another parameter that had a statistically significant relation with successful operative outcome was blood urea to serum creatinine (p-value < 0.01), the estimated OR was 27.9 (p-value < 0.01, 95% CI 17.4 – 44.8).

We also analysed the predictive value of other laboratory parameters. Using logistic regression statistical analysis, we found that other laboratory parameters were not statistically significant predictors of the successful outcome of OU operation ( Table 4).

OU is one of the most common emergency cases in urology. Among all patients discharged with urinary tract symptoms, OU was accounted to be around 0.9%-3.8% overall. ¹ The effect of a widespread population across the archipelago of Indonesia, the education level, and delayed presentation of referred patients cause patients’ condition to get worsened over time. Definitive treatment of upper-tract obstruction, such as double J stent and percutaneous nephrostomy insertion, would relieve symptoms and release urinary tract internal pressure. ¹

OU is a urinary tract disorder caused by impeded urine flow. It can be structural or functional in nature. Hydronephrosis occurs when urine backs up unilaterally or bilaterally into the kidneys, depending on the location of the obstruction. The obstruction may manifest itself in a variety of ways, but commonly includes difficulty initiating micturition or lower stomach discomfort and distention. ⁸ The goal of treatment is to alleviate the obstruction, either by re-establishing normal urinary flow within the urinary tract using a ureteral stent for upper urinary tract obstruction or by diverting the urine using a percutaneous nephrostomy tube. ⁹ However, After definitive treatment or urine diversion, there is no guarantee that renal function will be restored. This study was designed to find predictive laboratory parameters of the success of OU surgical treatment. Predictors such as the laboratory value describing renal function, did not show significant results. It might be caused by the delayed treatment by the effect of late presentation of patients to our center, thus resulting in irreversible damage of kidney function.

This study found out that renal parenchymal thickness plays an important predictive role in operative treatment success of OU, whether using nephrostomy or insertion of a double J stent. A good parenchymal thickness (between 14-18 mm) ³ of the obstructed kidney has a greater chance of successful OU treatment (p-value < 0,05), with an odds ratio of 11.34. Several previous studies have also reported that good renal parenchymal thickness affects the return of renal function after OU is relieved.

The collecting system's hydrostatic pressure increases when the urine's outward flow is blocked. As a consequence, the intraglomerular pressure rises, which affects the glomerular filtration rate. The duration and severity of the blockage affect how much renal function is lost. If the blockage is left untreated, it may result in renal scarring, irreversible kidney damage, a decline in glomerular and tubular function, and permanent kidney damage. As a consequence, if kidney function recovers to normal once a blockage is removed, hydronephrosis might be categorized as acute. ¹⁰ In situations of acute obstructive uropathy, immediate decompression is required, either anterogradely with the implantation of a ureteral stent or percutaneously with a nephrostomy tube. This decompression stops the inflammation, ischaemia, and further deterioration of renal parenchyma that might lead to chronic kidney disease that is irreversible. ¹¹

In contrast, even if the blockage is removed, kidney function does not return in chronic hydronephrosis. Long-term blockage results in a dilated collecting system, papillae compression, and parenchyma thinning, which eventually leads to cortical atrophy and tubulointerstitial fibrosis. Some of the physiologic impacts include impaired salt reabsorption, disturbance of urine acidification leading to metabolic acidosis, and impaired urinary concentrating capacity. A study by Bundu et al. (2018), showed that renal parenchymal thickness of more than 10 mm was correlated with successful post-operative recovery of renal function. ⁹ Another study by Roger et al. (1994) also reported that with a renal parenchymal thickness of 10-15 mm, there was a reversible change in terms of renal function after OU was relieved. ¹² Khalaf et al. (2004) also reported the same finding of a statistically significant relationship between good renal parenchymal thickness and successful OU operation. ¹³ Both study results are in line with what our study findings regarding renal parenchymal thickness. In the etiology of hydronephrosis, a reduction in cortical thickness may suggest atrophy. Thicker parenchymal and cortical thickness are linked to greater renal function recovery potential. ^{14 , 15}

Blood urea to creatinine ratio is associated with the reduction of serum creatinine reduction following urinary diversion procedures in OU. The delayed treatment of a presenting patient might be the cause of the alteration of blood urea to creatinine ratio as the estimation of severity of kidney injury. This finding is also in line with the study by Bundu et al. (2018), which reported that a ratio of blood urea to serum creatinine > 10 can be used as a prognostic factor to predict a successful OU therapy. ⁹ In Uchino et al. (2012), the ratio of blood urea to creatinine could differentiate pre-renal and intra-renal cause of kidney failure. High blood urea to creatinine level holds to pre-renal causes, such as cardiovascular events and massive hemorrhage. On the other hand, acute tubular necrosis could possibly be identified by a low blood urea to creatinine ratio. Low blood urea to creatinine ratio also had a lower chance of hospital mortality rate. ¹⁶ The median value of urea to creatinine ratio in our study was 24.14, with a minimum value of 7.3 and maximum value of 77.8. Although the majority of successful OU operations had a urea to creatinine ratio value higher than 10, several subjects had a ratio under 10 and a better renal function after OU was treated. Thus, further analysis is needed to assess other factors that might be affecting this finding and to pinpoint the minimal ratio that can predict renal function reversibility after the OU is relieved.

In this study, we found out that laboratory parameters of haemoglobin, haematocrit, leucocyte, thrombocyte, pre-surgery blood urea and creatinine levels, and electrolytes were unable to predict the successful outcome of OU surgical treatment. However, several other studies have found different results. Bundu et al. (2018), found that pre-operative haemoglobin levels greater than 10 mg/dL and blood urea to creatinine ratio greater than 10 was positively associated with recoverability of renal function after OU surgery. Another study by Sharma et al. (2015) revealed that pre-operative serum creatinine level of less than 1.5 mg% also correlated with reversible kidney function. ¹⁵ Multiple factors can cause this different finding, including patient’s characteristic (race, history of previous disease, and duration of obstruction) from each study. ^{17 – 19} Thus, further research about laboratories parameter that can predict reversibility of kidney function following OU surgical relieved is needed. The meta-analysis study of several wider laboratory parameters, followed with clinical trials for further analysis would be ideal to find other laboratory parameters predicting kidney function relief.

The clinical impact of this study is significant, considering it used a large sample size to analyse the predictive role of several parameters in determining a successful OU relieve operation. However, this study had several limitations, including a short period of follow up and the data was collected at a single health centre.

As our study involved more than 500 subjects, it would be the largest study of this type performed in Indonesia. However, as the analysis was carried out at a single centre, and as no prospective follow-up was done, more comprehensive data collection and subject observation method should be undertaken.

There were statistically significant relationships between renal parenchymal thickness and blood urea to serum creatinine level with a favourable operational outcome in OU, as evidenced by a reduction in postoperative creatinine.

The data availability is restricted for research purpose due to ethical issues and hospital regulation. The data can be accessed by request to the corresponding author, if needed for conducting further studies.