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Definitions used in lower urinary tract symptoms 

Definitions used in lower urinary tract symptoms
Definitions used in lower urinary tract symptoms

Hashim Hashim

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Key points

  • Nocturia is defined as the complaint that the individual has to wake at night one or more times to void. It has to be preceded and followed by sleep.

  • It is part of storage lower urinary tract symptoms.

  • It is important to differentiate nocturia from nocturnal enuresis which is wetting the bed at night whilst asleep.

  • The definition of nocturia does not take into account the degree of bother or the aetiology.

1.1 Definitions

Lower urinary tract symptoms (LUTS) can be divided into storage, voiding, and post-micturition symptoms [1]. Storage symptoms occur when the bladder is filling with urine; voiding symptoms occur when the individual is voiding, and post-micturition symptoms occur after the person has finished voiding (Table 1.1).

Table 1.1 Definitions of lower urinary tract symptoms standardized by the International Continence Society

Storage LUTS


The complaint that the individual has to wake at night one or more times to void

Increased daytime frequency

The complaint by the patient who considers that he/she voids too often by day


The complaint of a sudden compelling desire to pass urine which is difficult to defer

Urinary incontinence

The complaint of any involuntary leakage of urine

Voiding LUTS

Slow stream

Reported by the individual as his or her perception of reduced urine flow, usually compared to previous performance or in comparison to others

Intermittent stream (intermittency)

The term used when the individual describes urine flow which stops and starts, on one or more occasions, during micturition


The term used when an individual describes difficulty in initiating micturition, resulting in a delay in the onset of voiding, after the individual is ready to pass urine

Straining to void

Describes the muscular effort used to either initiate, maintain, or improve the urinary stream. Suprapubic pressure may be used to initiate or maintain flow

Terminal dribble

The term used when an individual describes a prolonged final part of micturition, when the flow has slowed to a trickle/dribble

Post-micturition LUTS

Feeling of incomplete emptying

A self-explanatory term for a feeling experienced by the individual after passing urine

Post-micturition dribble

The term used when an individual describes the involuntary loss of urine immediately after he or she has finished passing urine, usually after leaving the toilet in men or after rising from the toilet in women

Adapted from Neurourology and Urodynamics, 21(2), Abrams et al., ‘The standardisation of terminology of lower urinary tract function: Report from the standardisation sub-committee of the International, pp. 167–178, Copyright (2002), with permission from John Wiley and Sons.

Nocturia is part of the storage symptoms and, in 2002, has been defined by International Continence Society (ICS) as the complaint that an individual has to wake at night one or more times to void. Prior to 2002, there was no official definition. In 2010, the ICS definition of nocturia has been slightly modified to the complaint of interruption of sleep one or more times because of the need to micturate. Each void is preceded and followed by sleep [2].

It is important to note that aetiology and bother are not part of the definition of nocturia. In other words, the definition does not include the cause of the nocturia. If a person wakes up every night because they have a partner who snores, or because they have noisy neighbours or a child who is crying, and they decide to pass urine during the night when they wake up, then, by definition, this is nocturia. It is, however, non-pathological nocturia, i.e. the definition does not take into account whether there is pathology or not. Even if pathology is included, nocturia has multifactorial aetiology, as will be seen in Chapter 2, and it would be difficult to include a definition for every pathology.

The current definition also does not include the degree of bother and impact on quality of life (QoL). Studies have shown that nocturia does not become bothersome until the individual gets up two or more times to void at night [3]. However, what the current definition aims to do is to standardize the usage of the term, and any extra information will have to be included in any form of communication that may account for the aetiology and degree of bother of nocturia.

1.2 Criteria for definition of nocturia

There are certain agreed criteria that need to be fulfilled before an individual is labelled as having nocturia. These include:

  1. 1. each void must be preceded and followed by sleep, i.e. the first morning void is not included when the number of episodes of nocturia is being counted (see example in Chapter 3)

  2. 2. it is independent of the trigger for waking

  3. 3. it depends on the time spent sleeping, and not on the time spent in bed, i.e. it does NOT include:

    1. i. voids after going to bed, but before going to sleep

    2. ii. voids that prevent from going back to sleep.

These criteria can be slightly confusing if a person goes to bed at 10 p.m. and reads a book, then passes urine at 10.30 p.m. and goes back to bed, and then falls asleep at 11 p.m.! This is part of night-time frequency, but NOT nocturia, because it has to be preceded and followed by sleep to be nocturia. If, however, after falling asleep at 11 p.m., the person wakes up at 3 a.m. and then goes back to bed to sleep, then this would be considered nocturia (see example in Chapter 3).

1.3 Terms related to nocturia

Nocturia and the associated terms (Table 1.2) are mainly derived from the bladder diary. It is important to note that it is not possible to treat patients who complain of nocturia without the use of a bladder diary, ideally over a 3-day period, e.g. ICIQ-Bladder Diary (see Chapter 3).

Table 1.2 Terms related to nocturia



Nocturnal urine volume

  • Total volume of urine passed during the night, including the first morning void. This is an important definition that can also be confusing! When calculating nocturia episodes, the first morning void is not included, because it is not followed by sleep. However, when calculating nocturnal volume, the volume voided from the first morning void needs to be included, as it is urine being stored in the bladder during the night

  • A nocturnal urine production of >6.4 mL/kg per sleep cycle is suggestive of nocturnal polyuria [4]

Rate of nocturnal urine production

  • Nocturnal urine volume/time asleep (i.e. night); measured in mL/min

  • More than 0.9 mL/min is suggestive of nocturnal polyuria (about 450 mL per 8 h of sleep)

Nocturnal polyuria

Nocturnal urine volume >20–33% of total 24-hour urine volume (age-dependent):

  • 33% in elderly, e.g. >65

  • >20% in younger individuals

  • 20–33% in ‘middle age’

Nocturnal polyuria index (NPI)

Nocturnal urine volume/24-hour voided volume

24-hour voided volume

Total volume of urine voided during a 24-hour period (1st void to be discarded; 24 hours begin at the time of the next void)

24-hour global polyuria

24-hour voided volume in excess of 2800 mL (in 70 kg person, i.e. >40 mL/kg)


The period of time between going to bed with the intention of sleeping and waking with the intention of arising

Night-time frequency

The number of voids recorded from the time the individual goes to bed with the intention of going to sleep to the time the individual wakes with the intention of rising. It relates to the total time in bed. Therefore, it is the number of voids recorded from the time of going to bed to the time of rising and includes:

  • voids after going to bed, but before going to sleep

  • nocturia episodes

  • voids in the early morning, but the individual goes back to bed but not to sleep

  • depends on the time in bed

First morning void

The first void after waking with the intention of rising

Maximum voided volume

The largest single voided volume measured in a 24-hour period

Nocturnal enuresis

Voiding or wetting the bed whilst asleep, i.e. the individual is unaware and is in a state of sleep and is not awake. In other words, it is urinary incontinence whilst asleep

Nocturia index (Ni)

  • Nocturnal urine volume/maximum voided volume [5]

  • >1: nocturia occurs because maximum voided volume is smaller than nocturnal urine volume

  • >1.5: nocturia secondary to nocturnal urine overproduction in excess of maximum bladder capacity, i.e. nocturnal polyuria

Nocturnal bladder capacity index (NBCi)

  • Actual number of nightly voids (ANV) minus predicted number of nightly voids (PNV) (PNV = Ni − 1) [6]

  • >0: nocturia occurring at volumes less than maximum voided volume

  • >1.3: reduced bladder capacity as a cause of nocturia. The higher the value, the more likely it is the nocturia is due to reduced bladder capacity

1.4 Conclusion

In 2002, ICS defined nocturia as the complaint that an individual has to wake up one or more times to void. This definition means that the person must be awake before each void and goes back to sleep after voiding.

The aim of the ICS definition was to standardize the nomenclature. Obviously, this definition is not without its limitations, the main one being that it does not differentiate between pathological and non-pathological causes of nocturia. Also it does not apply to shift workers who often have disrupted and poor sleep as their natural circadian rhythm is altered. Furthermore, individuals whose sleep is disturbed by their bladder, so that they go to the toilet but cannot get back to sleep again, are not included, even if that voiding episode leaves them tired.

Previous definitions, such as having at least two voids or three voids at night, attempt to encompass bothersomeness without specifically asking the patient ‘How much bother does getting up at night cause you?’.

Therefore, with this in mind, ICS suggested that nocturia is a ‘condition’, and not a ‘disease’, since a condition is defined as ‘a state of being, specifically in reference to physical and mental health or well-being’. A disease, on the other hand, is a condition of abnormal vital function involving any structure, part, or system. The understanding of the distinctions between the different terminologies is very important, and it is equally vital that all health care providers are speaking the same ‘language’ when it comes to nocturia, as this has implications when patients report ‘nocturia” and therefore on clinical trial results and on the treatment of patients. This distinction has to be clearly explained to patients when filling out frequency/volume charts as well.


1. Abrams P, et al. The standardisation of terminology of lower urinary tract function: report from the Standardisation Sub-committee of the International Continence Society. Neurourol Urodyn. 2002;21:167–78.Find this resource:

2. Toozs-Hobson P, et al. An International Urogynecological Association (IUGA)/International Continence Society (ICS) joint report on the terminology for reporting outcomes of surgical procedures for pelvic organ prolapse. Neurourol Urodyn. 2012;31:415–21.Find this resource:

3. Tikkinen KA, et al. Nocturia frequency, bother, and quality of life: how often is too often? A population-based study in Finland. Eur Urol. 2010;57:488–96.Find this resource:

4. Matthiesen TB, et al. Nocturnal polyuria and natriuresis in male patients with nocturia and lower urinary tract symptoms. J Urol. 1996;156:1292–9.Find this resource:

5. Weiss JP, et al. Nocturia in adults: etiology and classification. Neurourol Urodyn. 1998;17:467–72.Find this resource:

6. Burton C, et al. Reference values for the Nocturnal Bladder Capacity Index. Neurourol Urodyn. 2011;30:52–7.Find this resource: