Sodium.

Although the clinical manifestations of an abnormal serum sodium concentration are uncommon, imbalances in sodium and water occur frequently. The major indications for the determination of the serum sodium are those situations in which the signs and symptoms of hyponatremia or hypernatremia are likely. In other situations, unless the determination of the sodium concentration will change the clinical management of the underlying disorder, the serum sodium is not very useful, and consequently, should not be ordered as a routine test. Laboratory tests should primarily be used to confirm clinical suspicions. The majority of disorders in which imbalances in sodium and water occur can be diagnosed on clinical grounds, irrespective of the serum sodium concentration.