Hypothesis / aims of study
Underactive bladder (UAB) can be due to neurogenic, myogenic, ageing, diabetes mellitus and bladder outlet obstruction. The pathophysiology of UAB is still not known completely. Studies have shown that adenosine tri phosphate (ATP) and nitric oxide (NO) levels in detrusor muscle are altered in UAB’s. Very few animal studies like the one done by Munoz et al (1) have shown that the urinary ATP/NO ratio is decreased in UAB’s. Jun cho et al (2) showed that ATP levels in the urothelium of patients with underactive active bladder due to BPH was significantly lower than controls. But till date, there has been no study available which has evaluated the levels of both urinary ATP and NO in UAB’s in humans. So we have aimed to evaluate any association of urinary ATP/NO levels with UAB. We also evaluated the association of urinary ATP/NO levels with urodynamic parameters like PVR (post void residual), Pdet Qmax (detrusor pressure at maximum flow rate) and BCI (bladder contractility index).
Study design, materials and methods
This is a prospective observational case control study done from June 2017 to November 2018. Diagnosed cases of UAB due to various aetiologies based on urodynamic study (UDS) with BCI <100 were enrolled as cases. Healthy volunteers without any lower urinary tract symptoms (LUTS) were enrolled as controls. Patients already on prolonged catheter, with active UTI (urinary tract infection) and with chronic renal failure (S Cr>2) were excluded. After taking informed written consent, two freshly voided urinary samples were collected from study subjects and urinary ATP, NO levels were measured using separate ELISA kits (Qayee-Bio). Urine was collected in a sterile container, centrifuged for 20 min at 3000 rpm the supernatant was collected and stored in sterile tarsons tube and kept at -20 degree celsius. Before processing the sample was thawed at 37 degree Celsius. The concentration of standard diluents used in the NO test were 5000, 2500, 1200,625,312, 0 pg/ml and that of ATP were 500, 250, 120, 62.5, 31.2, 0 pg/ml. UDS parameters in cases like Pdet Qmax, PVR and BCI were recorded. For normally distributed data means of 2 groups were compared using Independent t-test, group comparisons were made with Chi-Sq test or Fisher’s exact test. In order to find the correlation between various parameters Pearson correlation co efficient was used.The priori vs. post hoc analysis showed adequate sample size and power of more than 80 % with various online tools.
A total of 30 cases and 20 controls were enrolled during the study period and both the cohorts are comparable as per age and sex (p value <0.05). The most common etiology in cases of UAB was benign prostatic hyperplasia (47 %) followed by idiopathic (30 %), neurogenic bladder (13 %), previous pelvic surgery (7%) and diabetes (3 %). The mean urinary ATP levels was significantly lower in cases compared to controls (542.86 ± 36.5 pg/µl vs 614.96 ± 26.99pg/µl, p value <0.001). But the mean NO levels was significantly higher in cases compared to controls (1234.83 ± 85.99 pg/µl vs 1124.43 ± 87.4 pg/µl, p value <0.001). The mean ATP/NO ratio in cases was significantly lower thanthat of controls (0.4418 ± 0.044 vs 0.5503 ± 0.051, p value <0.001) (Table 1). There was no statistically significant association of urinary ATP and NO levels with UDS parameters like PVR, Pdet Qmax and BCI.
Interpretation of results
Urinary ATP levels were significantly lower and urinary NO levels were significantly higher in UAB subjects compared to that of healthy controls. An ROC curve was generated for urinary NO levels (Figure 1) with an area under the curve of 0.828 suggestive of good separability between cases and controls. At a cut off of 1170.52 pg/µL, urinary NO levels had a sensitivity of 86.7% and specificity of 80% for diagnosing cases of UAB. The ATP/NO ratio was significantly decreased in underactive bladders.