In diabetes insipidus the body cannot hold on to water, so the kidneys pass large amounts of dilute urine. It comes from a lack of the hormone vasopressin (central type, now called arginine vasopressin deficiency) or from kidneys that do not respond to it (nephrogenic type).
Key symptoms
- Large amounts of pale urine, often over 3 liters a day
- Strong thirst and a craving for cold water
- Getting up many times at night to urinate
- Fatigue and poor sleep
- Confusion or weakness if drinking cannot keep up
What you find on exam
- Signs of dehydration: dry mouth, fast pulse, low blood pressure
- Weight and fluid balance
- Mental status
- Clues to the cause: recent head injury or brain surgery, visual field loss
- Medication history: lithium is a common cause of the nephrogenic type
Tests
- Low urine osmolality (often under 300 mOsm/kg) with high or high-normal serum sodium
- Serum sodium, glucose, calcium and potassium to rule out other causes
- Water deprivation test, then desmopressin to tell central from nephrogenic
- Copeptin level and pituitary MRI
Treatment basics
- Free access to water; never restrict fluids without supervision
- Central type: desmopressin by mouth, nose or injection
- Nephrogenic type: treat the cause, low-salt diet and a thiazide; amiloride for lithium cases
- Check sodium regularly to avoid low sodium on desmopressin
- Correct high sodium slowly in hospital
Red flags
- Serum sodium over 150 mmol/L with confusion
- Unable to drink, such as after surgery or with reduced consciousness
- Seizure or very low sodium on desmopressin
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.