Polyuria-polydipsia syndrome (thirst and passing large volumes of urine) in adults

Urine tests

• 24-hour urine collection to measure urine output (empty the bladder at the start, collect all urine until the same time the next day, final voids included).
• Urine dipstick (glycosuria, proteinuria, leucocytes)

Laboratory tests

• Plasma glucose
• Serum electrolytes (sodium, potassium)
• Serum calcium
• Serum creatinine with eGFR
• Urine osmolality on a spot sample (if polyuria confirmed)if needednon-French guidelineConfirmed polyuria without diabetes mellitus, hypercalcaemia, hypokalaemia or renal failure: a urine osmolality above 700 mOsm/kg excludes central diabetes insipidus ^[1]. Not reimbursed in France (outside the fee schedule).
• Serum lithium (if on lithium)if needednon-French guidelinePatient treated with lithium: lithium causes nephrogenic diabetes insipidus ^[1]. See the page "Treatment: lithium".

• Endocrinology opinion: distinguish AVP deficiency (central diabetes insipidus), AVP resistance (nephrogenic) and primary polydipsia by a dynamic test in a specialist setting (copeptin after arginine stimulation or hypertonic saline, or water deprivation test), then hypothalamic-pituitary MRI depending on the result.
• Do not perform a water deprivation test in the community.