Sodium, serum

Normal range: 135-152 mmol/L

Comment: Sodium is the major cation of extracellular fluid, responsible for almost half the osmolality of plasma (central role in the distribution of water). Low serum levels are caused by vomiting, diarrhea, sweating, inappropriate antidiuretic hormone secretion, edema, ascites and Addison’s disease. Hypernatremia is found in water depletion and Conn’s disease

Sample: Serum

Sodium, spot urine: See Sodium, 24hr urine