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Nocturia and nocturnal polyuria
Nocturia is waking at night to void, preceded and followed by sleep; the cause may be global polyuria, nocturnal polyuria or reduced bladder capacity, and a 3-day bladder diary is the test that tells them apart.
Why it matters in the exam
The exam shows an older person who gets up 3 times a night, and asks about evaluation or treatment. The bladder diary (frequency-volume chart) allows calculation: global polyuria — more than 40 mL per kg in 24 hours (diabetes mellitus, diabetes insipidus, high fluid intake); nocturnal polyuria — night volume above 33 percent of daily volume in older people (above 20 percent in the young), as in heart failure, leg oedema, sleep apnoea, kidney disease and evening fluids or diuretics; and reduced bladder capacity — BPH, OAB, retention or infection.
Treatment targets the cause: treat sleep apnoea, heart failure and diabetes; limit fluids, caffeine and alcohol in the evening; raise the legs in the afternoon when there is oedema; move a diuretic to the afternoon (about 6 hours before sleep); and with small bladder capacity — treat OAB or BPH. Nocturia in an older person raises the risk of falls and fractures, so it matters regardless of the urological disease.
In nocturnal polyuria not responding to behavioural steps, low-dose desmopressin can be used (for example 25 micrograms for women and 50 micrograms for men as a sublingual tablet). The main risk is hyponatraemia, especially at age 65 or over: sodium is checked before treatment, in the first week and after one month, and desmopressin must not be given to patients with heart failure, low sodium, global polyuria or high fluid intake. Nocturia with thirst and heavy drinking requires exclusion of diabetes mellitus and diabetes insipidus.
Key points
- A 3-day bladder diary separates the types.
- Global polyuria: more than 40 mL per kg.
- Nocturnal polyuria: above 33 percent at night in older people.
- Desmopressin — risk of hyponatraemia.
- Nocturia in the elderly — risk of falls.
Summary table
| Type | Definition | Examples | Treatment |
|---|---|---|---|
| Global polyuria | More than 40 mL per kg in 24 hours | Diabetes mellitus, diabetes insipidus, high intake | Treat the cause |
| Nocturnal polyuria | Night above 33 percent of daily volume in older people | Heart failure, sleep apnoea, oedema, evening diuretic | Behavioural; desmopressin with care |
| Reduced bladder capacity | Small frequent voids | OAB, BPH, retention | Treat OAB or BPH |
| Sleep disorder | Waking for another reason | Insomnia, pain | Treat the sleep problem |
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Sources
- EAU Guidelines on Non-neurogenic Male LUTS, 2025 edition — Nocturia and nocturnal polyuria
- International Continence Society: Standardisation of terminology in nocturia, 2019 — Definitions
- Campbell-Walsh-Wein Urology, 12th edition (2020) — Nocturia
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.