The relative incidence of detrusor instability and bacterial cystitis detected on the urodynamic-test day

Objective To determine whether patients with detrusor instability (DI) were more likely to have bacterial cystitis or significant bacteriuria on the urodynamic-test day than were women with a stable bladder. Patients and methods A catheter specimen of urine was cultured (overnight in air) from 862 consecutive women at the time of urodynamic testing. The upper urinary tract was imaged, with cystoscopy when indicated, to exclude upper tract lesions or malignancy. The percentage of patients with pure idiopathic DI and those with mixed DI/genuine stress incontinence (GSI), in whom the urine culture was positive, was compared with the percentage who had a stable bladder (pure GSI or urodynamically normal) and a positive urine culture, both for the entire dataset and for women aged > or < 65 years. Data were also analysed to detect the converse relationship; in those women found to have bacterial cystitis, the relative risk of being found urodynamically unstable or stable was determined. Results The likelihood of bacterial cystitis occurring in patients with idiopathic DI (5.6%) was significantly greater than that in patients with GSI (1.1%; P = 0.009, Fisher's exact test). The proportion of patients with DI and significant bacteriuria (15.4%) was significantly greater than that in patients with GSI (7.9%; P = 0.02). In patients with combined pure and mixed DI, bacterial cystitis was significantly more likely to occur (6.3%) than in GSI (P < 0.001), but bacteriuria was no more likely (12.5%, P = 0.09). Conversely, of those women found to have bacterial cystitis, the relative risk of having an unstable bladder was increased (+1.56), but for those with bacteriuria the relative risk of detrusor instability was not increased. Conclusion There was a significant association between idiopathic DI and bacterial cystitis, and we suggest that in some women with an unstable bladder, urinary infection may enhance detrusor contractility. Nevertheless, large-scale studies are needed of the temporal relationship between the onset of bacterial cystitis and the onset of DI.