To evaluate whether urodynamic investigation (UDI), the gold standard to assess refractory lower urinary tract symptoms (LUTS), is appropriate to select healthy volunteers with apparent normal lower urinary tract function as control subjects for comparative studies.

42 healthy subjects (22 women, mean age 32±10 years; 20 men, mean age 37±12 years) without LUTS were included into this prospective single-centre cohort study. All subjects recorded a 3-day bladder diary, completed validated questionnaires regarding LUTS, and underwent neuro-urological assessment as well as free uroflowmetry. Same session repeat UDI was performed according to “Good Urodynamic Practice” recommended by the International Continence Society, but using an air-charged instead of a water-filled catheter, and evaluated by a blinded investigator.

All 3-day bladder diaries, LUTS questionnaires, neuro-urological assessments and free uroflowmetries were within normal limits. Overall (either during the first or second UDI), same session repeat UDI revealed pathological findings in 71% (30/42): Detrusor overactivity was detected in 14% (3/22) and 30% (6/20), post void residual >100mL in 14% (3/22) and 25% (5/20), bladder outlet obstruction in 9% (2/22) and 20% (4/20) and detrusor sphincter dyssynergia in 77% (17/22) and 65% (13/20) of our women and men, respectively.

Repeatability of detrusor overactivity (κ = 0.78, 95% CI: 0.54–1.02) and detrusor sphincter dyssynergia (κ = 0.77, 95% CI: 0.55–0.98) showed substantial agreement between both UDIs. All other assessed urodynamic parameters had wide 95% limits of agreement for differences in the parameters indicating poor repeatability.

More than 70% of our healthy subjects showed pathological urodynamic findings. Although UDI is the gold standard to assess refractory LUTS, it seems not to be applicable in healthy subjects to define normal lower urinary tract function. Therefore, we do not recommend using UDI to select healthy control subjects.