Comparison of flowrates and voided volumes during non-instrumented uroflowmetry and pressure-flow studies in women with stress incontinence


  • Robert Pickard led the peer-review process as the Associate Editor responsible for the paper.
  • Conflict of interest: none.



The Blaivas–Groutz nomogram defines voiding obstruction in women using Qmax from the NIF and the maximum detrusor pressure (Pdetmax) from the PFS. The aim of this study was to understand the relationship between NIF and PFS maximum flow rates in women with stress incontinence.


We analyzed the UDS of 597 women with stress-dominant urinary incontinence. Each subject underwent a NIF and then a PFS. Mixed model was used to test the hypothesis that the relationship between flow rates and voided volume (VV) were similar for NIF and PFS.


There were 452 subjects with both NIF and PFS studies that met the inclusion criteria and had max flow rate (Qmax) for both NIF and PFS. The mean age was 53. Overall, higher VV were observed during PFS compared to NIF and subjects had higher Qmax with NIF compared to PFS. The relationship between Qmax and VV was significantly different between NIF and PFS (P < 0.004). At 200 ml, NIF Qmax was 14% higher than PFS Qmax and this difference increased to 30% at 700 ml.


The difference between PFS Qmax and NIF Qmax increases as VV increase. As a result, values from PFS and NIF cannot be used interchangeably as has been suggested in the Blaivas–Groutz nomogram for obstruction in women. Neurourol. Urodynam. 34:549–553, 2015. © 2014 Wiley Periodicals, Inc.