Causes of hyponatremia and their usual corresponding urine studies and urine output
| Volume status | Etiology | Urine osmolality | Urine sodium | ADH-dependent | Urine output |
|---|---|---|---|---|---|
| Hypovolemic | Volume loss (nonrenal) | > 100 mOsm/Kg | < 30 mmol/L | Yes | Decreased |
| Cerebral salt wasting | > 100 mOsm/Kg | > 30 mmol/L | Yes | Increased | |
| Diuretics | > 100 mOsm/Kg | > 30 mmol/L | Yes | Increased | |
| Euvolemic | Syndrome of inappropriate ADH | > 100 mOsm/Kg | > 30 mmol/L | Yes | Decreased |
| Low-solute state | < 100 mOsm/Kga | < 30 mmol/L | No | Variable | |
| Primary polydipsia | < 100 mOsm/Kg | Variable | No | Increased | |
| Reset osmostat | Variable | Variable | No | Variable | |
| Hypervolemic | Cirrhosis | > 100 mOsm/Kg | < 30 mmol/L | Yes | Decreased |
| Heart failure | > 100 mOsm/Kg | < 30 mmol/L | Yes | Decreased | |
| Kidney failure | > 100 mOsm/Kg | > 30 mmol/L | No | Decreased |
↵a The osmolality in a low-solute state can be higher in a concomitant hypovolemic state.
ADH = antidiuretic hormone