• Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)

Isotonic hyponatremia or pseudohyponatremia

• Hyperlipidemia
• Hyperproteinemia

Hypertonic hyponatremia

• Hyperglycemia
• Mannitol, sorbitol, glycerol, maltose
• Radiocontrast agents

Hypotonic hyponatremia

• Extrarenal salt loss (U_Na+ < 10 meq/L): dehydration, diarrhea, vomiting
• Renal salt loss (U_Na+ >20 meq/L): diuretics, ACE inhibitors, nephropathies, mineralocorticoid deficiency, cerebral sodium-wasting syndrome

• Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)
• Postoperative hyponatremia
• Hypothyroidism
• Psychogenic polydipsia
• Beer potomania
• Idiosyncratic drug reaction (thiazides, ACE inhibitors)
• Endurance exercise

• Congestive heart failure
• Liver disease
• Nephrotic syndrome (rare)
• Advanced renal failure