Differential Diagnosis of Water and Salt Balance Disorders
Core Pathophysiology
Mechanism Definitions
- SIADH: Inappropriate excess arginine vasopressin (AVP) action; impaired renal free water clearance.
- Cerebral Salt Wasting (CSW): Primary hypersecretion of natriuretic peptides causing excessive renal sodium excretion.
- Central Diabetes Insipidus (DI): Deficient AVP production causing unregulated renal free water loss.
- Systemic Dehydration: Primary systemic fluid and salt loss inducing hypovolemia.
- Primary Polydipsia: Compulsive, excessive water intake causing physiological AVP suppression.
Comparative Clinical and Biochemical Parameters
| Parameter | SIADH | Cerebral Salt Wasting (CSW) | Central DI | Systemic Dehydration | Primary Polydipsia |
|---|---|---|---|---|---|
| Intravascular Volume | Normal or High | Low (Hypovolemia) | Low | Low | Normal or High |
| Serum Sodium | Low (<135 mEq/L) | Low (<135 mEq/L) | High (>145 mEq/L) | High/Normal | Normal/Low |
| Urine Sodium | High | Very High (>150 mEq/L) | Low | Low (<20 mEq/L) | Normal |
| Urine Output | Normal or Low | High | High | Low | High |
| Blood Pressure | Normal | Decreased/Orthostatic | Decreased/Orthostatic | Decreased | Normal |
| Blood Urea Nitrogen (BUN) | Low | High | High | High | Normal/Low |
| Serum Uric Acid | Low | Normal or High | High | High | Normal |
| Vasopressin (AVP) Level | High | Low (Suppressed) | Low | High | Low |