Purpose: It has been reported that over 33 % of patients with OAB present with pyuria (≥10 wbc μl-1) on urine microscopy, but under a third of these have bacteriuria. To clarify this situation, an accomplished comparative scrutiny of the inflammatory state of the urothelium in OAB, was carried out. Materials and Methods: This was a prospective, blinded, observational study of idiopathic OAB patients compared with controls. CSU samples were obtained and submitted to fresh urine microscopy, routine culture and microscopic examination of spun sediment. Another sample of OAB patients and asymptomatic controls provided cystoscopic bladder biopsies for histopathology and electron microscopy. Results: 178 OAB patients and 21 controls provided spun sediment samples. 75 (42 %) of these OAB patients had microscopic pyuria (.1 wbc ƒÊl-1) with 25 of which (33 %) were culture-positive. None of the controls had pyuria, nor bacteriuria. In a 20 mm2 spun deposit there was an average of 48 wbc (95 % CI 26 to 589) in OAB with pyuria; 12 wbc (95 % CI 10 to 15) in OAB without pyuria; and 4 wbc (95 % CI 3 to 7) in controls. Biopsies from 79 OAB patients, showed chronic inflammation and hyperplasia in 69 (87 %; 95 % CI=78 to 92: only 20 % had pyuria) and none in 5 controls. EM of 22 OAB patients showed increased basement membrane thickness compared to 2 controls (H=48, df=2, p<0.001). Conclusions: The study shows evidence of chronic cystitis and urothelial hyperplasia associated with OAB irrespective of pyuria or bacteriuria. The phenomenon has been confirmed by 3 different methods
