Diabetes Insipidus vs. Syndrome of Inappropriate Antidiuretic Hormone (SIADH)
Prepared by Fidel Lim
Common Causes
Pathophysiology
Diagnosis
Manifestations
Urine output
Serum Sodium
DI
Brain injury/surgery/tumor
(neurogenic/central), inadequate
renal response to ADH
(nephrogenic), excess water
intake (primary)
Lack of ADH
Lab values (see below), water
deprivation test
Dilute urine
Altered mental status
Polyuria - Up to 20 liters/day = can
lead hypovolemic shock
High (which can lead to cerebral
shrinkage) = neuro changes
Serum Potassium
Serum Osmolality
Urine Osmolality
Urine Specific Gravity
Weight
Medicine/Treatment
Variable, could be increased
High (greater than 295 mOsm/L)
Low
Low (typically <1.0005)
Loss
Synthetic antidiuretic hormones
(desmopressin), chlorpropamide,
and carbamazepine
If treatment works
Urine output will decrease and
return to normal amount
Fluids
Increase intake (oral or IV)
Other
Monitor weight
SIADH
Small cell lung cancer, head
injury, brain tumors, thiazide
diuretics, SSRI, pneumonia,
TB, GBS, brain infections
Too much ADH
Lab values (see below)
Concentrated urine
Altered mental status
Reduced = can lead to
pulmonary edema
Low (dilutional hyponatremia)
which can lead to cerebral
edema) = neuro changes
Variable
Low (less than 275 mOsm/L)
High
High
Gain
ADH antagonist (conivaptan,
tolvaptan). If sodium is
critically low give hypertonic
saline (3%). Loop diuretics
may be use. Increase salt in
the diet
Urine output will improve or
increase and sodium returns
to normal
Restrict Intake (800-1000
mL/day)
Monitor weight