Patients told to arrive with a full bladder for uroflowmetry or ultrasound sometimes drink litres of water in a short time. In older men, especially those on thiazides or SSRIs, that can cause severe hyponatraemia, confusion and seizures.
The fix is clear, specific instructions.
- Give a measured instruction — for example, 500 mL to 1 L of water over the hour before the test.
- Tell patients not to keep drinking if they cannot void or feel unwell.
- Take extra care in older adults on thiazides, SSRIs or with heart or kidney disease.
- Consider hyponatraemia in a patient who becomes confused, vomits or fits in the waiting area.
Why it matters
A routine test instruction can cause a dangerous, preventable electrolyte emergency.
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