Sodium

Sodium is the predominant extracellular cation. Serum sodium level is primarily determined by the volume status of the individual. Hyponatremia can be divided into hypovolemia, euvolemia, and hypervolemia categories.

Normal Range: 135-145 meq/L

increased in: Dehydration (excessive sweating, severe vomiting or diarrhea), polyuria (diabetes mellitus, diabetes insipidus), hyperaldosteronism, inadequate water intake (coma, hypothalamic disease). Drugs: steroids, licorice, oral contraceptives.

 

Decreased in: Congestive heart failure, cirrhosis, vomiting, diarrhea, excessive sweating (with replacement of water but not salt); salt-losing nephropathy, adrenal insufficiency, nephrotic syndrome, water intoxication, SIADH. Drugs: thiazides, diuretics, ACE inhibitors, chlorpropamide, carbamazepine. 

 

Additional: Spurious hyponatremia produced by severe lipemia and hyperproteinemia if sodium analysis involves a dilution step. Sodium falls about 1.6 mmol/L for each 100 mg/dL increase in blood glucose. Hyponatremia in a normovolemic patient with urine osmolality higher than plasma osmolality suggests the possibility of SIADH, myxedema, hypopituitarism, or reset osmostat.