Sodium (Na)

Indications for performing this test:  Sodium is one of the electrolytes included in a standard serum biochemistry panel.  Serum sodium is most reflective of the status of the body fluids, rather than sodium itself.

    A standard serum biochemistry panel will include Na, K, and Cl.  These important electrolytes should all be considered together along with any acid base abnormalities and the anion gap.  Although an electrolyte pattern is rarely diagnostic, it is useful in the assessment of the severity of body fluid disorders and may be very important in the implementation of fluid therapy.  Sodium is the primary ion in the extracellular fluid.  Its concentration is regulated by aldosterone, atrial natriuretic factor, and antidiuretic hormone.

Hypernatremia

• ***Usually the result of dehydration.  This requires hypotonic water loss, where water is lost without loss of Na.  Diabetes insipidus may cause hypernatremia***

• Marked elevations in Na will occur in the face of dehydration paired with restricted access to water or impaired thirst mechanisms.

• Salt poisoning:  Rare except in swine.

• Primary adipsia:  Also rare

• Hyperadrenocorticism:  Slight increases.

• Shift of water without Na:  Gastrointestional pooling of water occurs in ruminants with grain overload-lactic acidosis.

Hyponatremia

• ***Associated with the loss of Na rich fluids or retention of Na free water as in heart failure or some ascitic diseases***

• Hypoadrenocorticism.

• Diarrhea:  This is especially a concern in horses.

• Renal disease:  Because Na is reabsorbed in the tubules, renal tubular disease can cause Na wasting.

• Iatrogenic:  Treatment with low sodium fluids.

• Diabetes mellitus.

• Third space loss:  Ascites may cause Na to pool outside of the vasculature. 

• Artifact of photometer determination of Na concentration:  Occurs with lipemia or hyperproteinemia.