Impact of Weight Based Versus Diary Based Filling Rate on the Accuracy of Invasive Urodynamics in Patients With...

Bladder filling rate has the potential to significantly impact the results of a urodynamics study (UDS). The International Continence Society (ICS) recommends two methods to determine the filling rate: Body weight divided by 4 (BW/4) and 10% of maximum voided volume (MVV) (10%MVV) from a bladder diary. However, there is no evidence if one method is superior to the other.

This prospective study included patients undergoing UDS for non-neurological diseases, and the filling rate was calculated using both formulas. The study cohort consisted predominantly of patients with voiding lower urinary tract symptoms (LUTS). All the patients underwent UDS twice-once with the filling rate calculated by BW/4 method and once with the 10% MVV method. All UDS parameters, including the maximum cystometric capacity (MCC) were recorded and compared between the two methods used to calculate the fill rates. The MCC recorded during the UDS, with both methods, was further compared with the patient's MVV documented on the bladder diary to assess its accuracy.

The study included 31 patients, and the calculated fill rate by the BW/4 method was 16 mL/min, and that with 10%MVV was 33 mL/min. The MCC on the UDS was 323 mL (IQR: 238-422) for the BW/4 method and 348 mL (IQR: 236-430) for the 10% MVV method, with no statistically significant difference from the MVV as recorded on the bladder diary (p = 0.961 and p= 0.549, respectively). Other urodynamic parameters, including first sensation, first desire to void, strong desire, bladder compliance, and detrusor overactivity, also showed no significant variation between the two methods to calculate the filling rate.

Both the BW/4 and 10% MVV formulas provide reliable estimates of MCC and do not significantly alter the urodynamic parameters. While the BW/4 method better aligns with the physiological filling rates, the 10% MVV method can result in faster filling and shorter duration of the urodynamic study, without adversely affecting its quality. These findings, however, may not apply to patients with storage LUTS, and studies in more diverse populations are warranted.