Evaluation of the etiology of nocturia in men: The nocturia and nocturnal bladder capacity indices

To determine and quantify the cause of nocturia in men, we describe and eva luate the relative contribution of two complementary indices of nocturia: t he nocturia index (Ni), a measure of nocturnal urine overproduction, and th e nocturnal bladder capacity index (NBCi), reflective of nocturnal bladder capacity. The records of 100 consecutive men with lower urinary tract sympt oms (LUTS), having undergone video-urodynamic studies (VUDS), were prospect ively studied. Evaluation included American Urological Association symptom score (AUASS), micturition diary (day, night, and 24-hr voided volume), and VUDS. Voiding diary analysis was carried out as previously described by us , determining the Ni, NBCi, and nocturnal polyuria index (NPi) (nocturnal u rine volume/24-hr urine volume). In the case of AUASS question #7 (degree o f nocturia), the odds of having a severe AUASS question #7 response was fou nd to be 4.09 times higher for patients with NBCi >2.0 compared with patien ts whose NBCi was less than or equal to 2.0 using logistic regression analy sis. In comparing patients with severe nocturia and low NBCi with those hav ing mild nocturia and low NBCi, Ni performed in a fashion superior to NPi i n identifying relative nocturnal urine overproduction as the suspected expl anation for their nocturia(Ni = 3.42 vs. 1.42, P = 0.0002 cf. Npi = 0.44 vs . 0.27, P = 0.018, Mann-Whitney test, respectively). We suggest a discrimin ating threshold of NBCi > 2 as highly significant in defining diminished NB C as a factor in the etiology of nocturia. In addition, we propose Ni of 1. 5 as a threshold greater than which nocturia may be attributed to nocturnal urine overproduction in excess of maximum bladder capacity. Together, thes e indices describe in quantitative fashion the relative contributions of no cturnal urine overproduction and diminished NBC in identifying the etiology of nocturia in male patients. (C) 1999 Wiley-Liss, Inc.