Urine flow rate measurements are generally used to determine lower urinary tract (LUT) dysfunction. We have previously established normal reference values for maximum (Qmax) and average urine flow (Qave) in children. Decreased acceleration of the detrusor muscle contraction (Qacc) may be an appropriate indicator for the early signs of autonomic neuropathy in children and adolescents with type 1 diabetes [1,2]. Qacc has also been found to be superior to Qmax in the diagnosis of bladder outlet obstruction in adult men with benign prostate hyperplasia [3]. A possible damage in the detrusor muscle function may also impair Qacc. Since there is no consensus on the cut-off values of Qacc in pediatric population which limits the use of Qacc, our aim was to establish normal ranges of it in both genders by voided volumes.

Data were collected from healthy children who underwent uroflowmetry. Children were divided into those with body surface areas of <0.92 m2, between 0.92 and 1.42 m2, and > 1.42 m2. Exclusion criteria were voided volume less than 20 ml, and postvoid residual more than 15%. Baseline characteristics and uroflowmetry parameters were collected from girls and boys aged between 6 and 18 years. Voided volume, voiding time, time to maximum flow rate, Qmax and Qave were measured, and Qacc was calculated. Postvoid bladder diameter was measured by ultrasonography and converted to volume. Quantile method was used to establish the 3–97th percentile levels with SPSS (version 25.0, Armonk, NY: IBM Corporation, US) statistical software package. The centile curves of acceleration by voided volume were estimated by using lmsChartMaker Pro 2.3 (Medical Research Council, UK 1997–2006; Cole and Green 1994; Cole and Pan 2004) software based on the LMS method. The study is reported as per the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) 2004 Statement.

Uroflowmetry parameters of 208 children (≤18 years old, 45.2% girls, mean age 9.68 ± 3.09 years) who performed 404 micturition were analyzed. Median voided volume, voiding time, time to Qmax, Qave, Qmax, Qacc, and postvoid residual volume were 130 [20–460] ml, 10 [3–56] s, 3 [1–14] s, 11.7 [2.5–36.6] ml/s, 20.5 [5–50] ml/s, 6 [0.81–25] ml/s2 , and 1.83 [0–38.62] ml, respectively. Qacc nomograms were given in centile forms for each body surface area group in both girls and boys, which show an inversely proportional correlation between voided volumes.

As acceleration of urine flow can provide a finer diagnosis of abnormalities of the LUT and various chronic diseases (diabetes mellitus etc.), our results could form a basis on studies about the diagnostic significance of uroflow parameters in different diseases in children.
These are the first nomograms for normative reference values of Qacc in the pediatric population in centile forms. These may be useful to interpret abnormal Qacc values and diagnose LUT diseases over a wide range of voided volumes.

Since there are only a few studies evaluating Qacc in adult and pediatric population with different diseases, and normative reference values of it are lacking, we found it important to establish normal ranges of Qacc in both genders by voided volumes in children. Since we evaluated the Qacc patters of healthy asymptomatic pediatric population, we formed the basis of future prospective studies. Prospective studies comparing healthy children and pediatric population of different diseases with or without LUT symptoms will be needed to establish cut-off values to differentiate normal and abnormal uroflow patterns.

1.	Szabo L, Barkai L, Lombay B: Urinary flow disturbance as an early sign of autonomic neuropathy in diabetic children and adolescents'. Neurourology and Urodynamics 2007, 26:218-221.
2.	Barkai L, Szabó L: Urinary bladder dysfunction in diabetic children with and without subclinical cardiovascular autonomic neuropathy. Eur J Pediatr 1993, 152:190-192.
3.	Wen JG, Cui LG, Li YD, Shang XP, Zhu W, Zhang RL, Meng QJ, Zhang SJ: Urine flow acceleration is superior to Qmax in diagnosing BOO in patients with BPH. J Huazhong Univ Sci Technolog Med Sci 2013, 33:563-566.