Nocturia is the condition when an individual has to wake at night one or more times for voiding [1]. Its causes are varied, and in many patients, its cause is difficult to discern. Nocturia is associated with ageing, behavioral influences (e.g., late-night fluid intake and consumption of caffeine) or several medical conditions (e.g., diabetes, congestive heart failure, lower urinary tract obstruction, prostatic disease, and overactive bladder) [2]. Although nocturia can occur at any age, it is more common among older adults, and was the most commonly reported storage symptom for both men and women in five European countries [3]. The overall prevalence rates for nocturia range from 10.8% to 25% in men and increase with age [45], and the most frequent concern regarding nocturia in elderly individuals is that rising at night to urinate could induce traumatic falls that lead to prolonged morbidity [6]. Additionally, Shao et al. [7] reported that nocturia plays an important role in patients younger than 65 years of age in daytime dysfunction, which should not be overlooked.

Because nocturia affects a significant proportion of adults and has a detrimental effect on health-related quality of life, the impact, cause, and result of lower urinary tract symptoms (LUTS) and nocturia have been widely studied in North America and Europe [8]. In Japan, Yoshimura et al. [9] reported that benign prostate hyperplasia was an independent positive risk factor for nocturia. However, in Korea, few studies have evaluated nocturia, especially with the frequency volume chart and international prostate symptom score (IPSS) in men. The frequency volume chart is a simple but essential for measuring the outcomes in clinical trials of interventions for LUTS [10]. A 3-consecutiveday chart is widely used to assess patients' voiding patterns.

In an effort to collect cornerstone data for treatment of nocturia in Korean men, the present study was conducted to assess the categories of nocturia by analyzing the frequency volume chart in male patients with LUTS accompanying nocturia one or more times a day and relationships with IPSS in Korean men.

Five hundred twenty-one patients from five different hospitals were included in this study.

Nocturia is the most bothersome of all LUTS, and it is most strongly associated with reduced quality of life, as evaluated by health-related quality of life questionnaire [12131415]. The International Continence Society defines nocturia as the condition when an individual must wake at night one or more times to void. Two or more episodes are generally considered as being clinically significant, as this threshold is the one that is associated with reduced quality of life [16]. Because of the clinical impact of nocturia, the classification, prevalence, therapeutic modalities, and outcomes have been widely studied in Western countries. However, little is known about nocturia in East Asian countries including Korea [917]. The problem is that most elderly individuals consider nocturia as a normal part of the ageing process that does not need treatment. Moreover, a very small proportion of patients with nocturia have sought medical care [18], and only 63% of them were offered treatment because physicians are still unfamiliar or concerned about the impact of nocturia [11].

In this study, we observed many distinctive results. The baseline characteristics showed that age and nocturia have a strong positive correlation, as Wang et al. [17] reported. Additionally, the first sleep period and FBC decreased with age and nocturia events. Overall, 71.2% of patients had nocturnal polyuria, and all their voiding parameters were different from those of patients without nocturnal polyuria, except the NBCI. These data were consistent with those of Matthiesen et al.' s study [19] and Weiss et al.'s report [2] that nocturnal polyuria was a significant component of nocturia in 43% of patients, most of whom had reduced NBC.

When considering the relationships of the frequency volume chart with IPSS, each IPSS questionnaire (2, 4, and 7) and subtotal storage symptom scores were correlated with the number of nocturia events. Moreover, we observed a reduced NBCI more in the group with a severe IPSS.

The ICIQ-N is a simple diagnostic tool that can measure the burden caused by the frequency of daytime and nighttime voiding. Eckhardt et al. [20] reported that nocturia was one of the most bothersome symptoms in male patients with LUTS, and our data measured by the ICIQ-N was consistent with their finding. Furthermore, our study showed that nocturia was the prominent bothersome factor for sleep quality.

The LUTS assessment with questionnaires can be affected by recall bias. In the real-time clinical setting, a difference or poor correlation between the 3-day frequency volume chart and patient's perception can be easily observed. Thus, the real-time completion of documentation is important to obtain accurate voiding function and reduce recall bias. Although the frequency volume chart cannot replace a urodynamic study, it is crucial for recognizing the condition of a patient's bladder function.

This study has a couple limitations. Comorbidities such as cardiovascular disease, central nervous system disease, peripheral edema or hypertension, and diabetes mellitus were not considered. Additionally, we could only identify the characteristics of patients in some areas of the country; thus, the enrolled patients who visited the tertiary hospitals do not represent the general population. Despite those limitations, the number of study subjects was sufficient to represent general baseline populational data. Further nationwide study is needed to collect and analyze data of nocturia in Korea.

Nocturia has a wide etiology, and it has a crucial impact on quality of life. Despite the importance of nocturia, the prevalence and classification of nocturia in Korea is still lacking. This is the first large multicenter study of Korean male patients with LUTS and nocturia that assessed the frequency volume chart, IPSS, and ICIQ-N. Our data showed that in Korean male LUTS patients with nocturia, the mixed type of nocturia was prominent, and patients with a higher IPSS showed much lower sleep quality than those with a lower IPSS. Korean male nocturia patients with LUTS also have a reduced NBCI. In addition, we found that the first sleep period and FBC are negatively correlated with nocturia, whereas the IPSS and ICIQ-N are positively correlated with nocturia. The nocturia score of the IPSS could be a predictive factor for a high total IPSS, high storage score, and poor sleep quality. This manuscript provides concrete evidence that proper nocturia managements with reduced nocturnal bladder capacity and nocturnal polyuria could improve patients' quality of life as well as sleep quality.