Pressure-flow nomogram for women with lower urinary tract symptoms

Results of urodynamic studies performed in female patients are often difficult to interpret. The objective of the study was to develop a nomogram that would help in diagnosing functional bladder outlet obstruction (BOO) in neurologically intact women with any kind of lower urinary tract symptoms.

From the urodynamic database adult women were chosen with maximal flow rate (Q max ) ≤ 12 ml/s in a pressure-flow study. Four criteria were used to identify a group of patients suspected of BOO: thickened bladder wall, presence of bladder diverticula, subjective improvement on α-blockers and improvement of voiding symptoms on any form of treatment. The line separating high and low pressure zones on the pressure-flow chart was established according to the position of patients who met at least one of them.

Sixty-seven patientswere investigated. Twenty-one women met at least one of the specified criteria. They had significantly higher voiding pressures (p det(Qmax) 35 cm H2O vs. 16.5 cm H2O; p = 0.002). A new nomogram with one separating line (p det(Qmax) = 1.5 × Q max + 10) was proposed. The difference in the distribution of women fulfilling the criteria between high pressure zone and low pressure zone was highly significant (19/35 vs. 2/32; p < 0.0001). Sensitivity, specificity, positive and negative predictive values of our nomogram in identifying patients suspected of BOO was 90.5%, 65.2%, 54.3% and 94% respectively.

The new nomogram can be considered a screening test which efficiently excludes obstruction among women with low Q max in a pressure-flow study.