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Diabetes Insipidus vs Syndrome of Inappropriate ADH (SIADH) - Comparison Table

Diabetes Insipidus - Inadequate ADH
SIADH -
Inappropriate ADH ... (SIADH) - Comparison ... SIADH - Excess ... ADH #Diabetes ... #Insipidus #SIADH
Cerebral Salt Wasting vs SIADH - Pathophysiology 
1) Neurological event
2) Sodium loss from tubules
3) Naturiesis →
Salt Wasting vs SIADH ... Hypovolaemia → ADH ... #SaltWasting #SIADH
Physiologic Approach to Hypotonic Hyponatremia
The next time you have a case of hypotonic hyponatremia, give the
restriction alone in SIADH ... Ineffective (UNa >30) • ADH ... Present (Uosm ≥100): SIADH ... Salt Wasting • ADH ... intake, UNa <20) • ADH
Urine Specific Gravity - Interpretation
Specific Gravity = Density of urine / Density of water
SG close to
resistance to ADH ... Dehydration • SIADH ... inappropriate ADH
Hyponatremia - Differential Diagnosis Algorithm
ADH Independent:
 • Tea and Toast Syndrome, Beer Potomania - Low solute
Diagnosis Algorithm ADH ... ADH Dependent: ... insufficiency, SIADH
Modified Hyponatremia Algorithm
Hypertonic Hyponatremia: Hyperglycemia, Mannitol, Urologic irrigants
Hypotonic Hyponatremia: 
 • ADH ON (UOsm > 100):
Hyponatremia: • ADH ... OFF (UNa > 30): SIADH ... salt wasting • ADH
Hyponatremia Differential Diagnosis Algorithm - Utilizing Uric Acid 
ADH promotes Urea/uric acid excretion along with water
Utilizing Uric Acid ADH ... Low Uric Acid → SIADH
Hyponatremia - Differential Diagnosis Algorithm
Hypovolemic - Give volume
Hypervolemic (Edematous) - Look for and treat underlying cause
• UOsm > 300 - ADH ... - Appropriate ADH ... , SSRIs) - SIADH
Hyponatremia - Differential Diagnosis by Mechanism
Decr Blood Pressure (“Decr Effective Circulating Volume”) 
 - Volume depletion
Inappropriate ADH ... secretion (SIADH ... insufficiency ADH
Hyponatremia Treatment Algorithm

CHF, Cirrhosis - Fluid restriction
SIADH - Fluid restriction
 - Consider salt tablets if etiology
Fluid restriction SIADH ... status turns off ADH