Diabetes insipidus is a disease in which large volumes of dilute urine (polyuria) are excreted due to vasopressin (AVP) deficiency [central diabetes insipidus (CDI)], AVP resistance [nephrogenic diabetes insipidus (NDI)], or excessive water intake (primary polydipsia). Polyuria is characterized by a urine volume in excess of 2 l/m2/24 h or approximately 150 ml/kg/24 h at birth, 100–110 ml/kg/24 h until the age of 2 years and 40–50 ml/kg/24 h in the older child and adult.
Diabetes insipidus (DI) is defined as the passage of large volumes (>3 L/24 hr) of dilute urine (< 300 mOsm/kg). It has the following 2 major forms:
- Central (neurogenic, pituitary, or neurohypophyseal) DI, characterized by decreased secretion of antidiuretic hormone (ADH; also referred to as arginine vasopressin [AVP])
- Nephrogenic DI, characterized by decreased ability to concentrate urine because of resistance to ADH action in the kidney
Two other forms are gestational DI and primary polydipsia (dipsogenic DI); both are caused by deficiencies in AVP, but the deficiencies do not result from a defect in the neurohypophysis or kidneys.
Diagnosis of Diabetes Insipidus (DI)
If the clinical presentation suggests DI, laboratory tests must be performed to confirm the diagnosis, as follows:
- A 24-hour urine collection for determination of urine volume
- Serum electrolyte concentrations and glucose level
- Urinary specific gravity
- Simultaneous plasma and urinary osmolality
- Plasma ADH level
Additional studies that may be indicated include the following:
- Water deprivation (Miller-Moses) test to ensure adequate dehydration and maximal stimulation of ADH for diagnosis
- Pituitary studies, including magnetic resonance imaging (MRI) and measurement of circulating pituitary hormones other than ADH
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Created Sep 13, 2018.