Differentials
Psychogenic polydipsia
SIGNS / SYMPTOMS
Clinical signs and symptoms are similar.
Commonly associated with an underlying psychiatric disorder.[1]
Daytime symptoms only or waking at night with the need to drink rather than to pass urine is more suggestive of primary polydipsia.[3]
INVESTIGATIONS
Hyponatremia suggests primary polydipsia.
Water deprivation test: normal response to dehydration is a rise in urine osmolality to >700 mOsm/kg; however, longstanding polyuria secondary to primary polydipsia may limit renal concentrating ability.
Hypertonic saline stimulation test and measurement of copeptin: copeptin level >4.9 pmol/L.
Diabetes mellitus
SIGNS / SYMPTOMS
Clinical signs and symptoms may be similar.
INVESTIGATIONS
Plasma glucose elevated.
Diuretic use
SIGNS / SYMPTOMS
Clinical signs and symptoms may be similar.
History of diuretic use.
INVESTIGATIONS
Clinical diagnosis.
Hypercalcemia
SIGNS / SYMPTOMS
Usually asymptomatic. Patients may report abdominal pain, constipation, low mood, renal stones, fatigue, or anorexia.
INVESTIGATIONS
Serum calcium/corrected calcium elevated.
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