A three-day frequency-volume chart, recording the time and volume of every void and drink, is cheap, needs no equipment and often changes the diagnosis.
It separates nocturnal polyuria, where more than about a third of the 24-hour urine is passed at night, from a small-capacity or overactive bladder and from obstruction. Nocturnal polyuria points away from the prostate and towards evening fluid intake, diuretics timing, heart failure, sleep apnoea or poorly controlled diabetes.
- Ask the patient to record times and volumes of all voids and drinks for three days.
- Calculate the share of urine passed at night.
- Large night-time volumes suggest nocturnal polyuria rather than a prostate problem.
- Review evening fluids, caffeine, alcohol and diuretic timing.
- Check for oedema, sleep apnoea symptoms and glucose control.
Why it matters
Nocturia from nocturnal polyuria does not respond to prostate treatment, and the chart finds it.
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