Isotonic hyponatremia or pseudohyponatremia
(normal serum osmolality; artifact corrected in most U.S. labs)
- Hyperlipidemia
- Hyperproteinemia
Hypertonic hyponatremia
(serum osmolality >295 mosm/kg)
- Hyperglycemia
- Mannitol, sorbitol, glycerol, maltose
- Radiocontrast agents
Hypotonic hyponatremia
(serum osmolality < 280 mosm/kg)
Hypovolemic
- Extrarenal salt loss (UNa+ < 10 meq/L): dehydration, diarrhea, vomiting
- Renal salt loss (UNa+ >20 meq/L): diuretics, ACE inhibitors, nephropathies, mineralocorticoid deficiency, cerebral sodium-wasting syndrome
Euvolemic
- Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)
- Postoperative hyponatremia
- Hypothyroidism
- Psychogenic polydipsia
- Beer potomania
- Idiosyncratic drug reaction (thiazides, ACE inhibitors)
- Endurance exercise
Hypervolemic
(edematous states)
- Congestive heart failure
- Liver disease
- Nephrotic syndrome (rare)
- Advanced renal failure