Serum Electrolytes

What are electrolytes?

Electrolytes are the salts and metallic components that are dissolved within the blood serum (serum is the liquid portion of blood). The electrolytes of greatest clinical importance are sodium, potassium, chloride, bicarbonate, phosphorus, and calcium.

Why are electrolytes important?

Electrolytes are involved in most of the body's daily functions. For example, electrolytes are required for proper nerve conduction, for heart and skeletal muscle contraction, for maintenance of proper hydration, and for maintenance of proper blood pH.

What samples are needed to measure electrolytes?

A single blood sample is all that is required for electrolyte determination. This sample may be analyzed in the veterinary clinic or sent to a veterinary referral laboratory for electrolyte determination.

What do changes in electrolyte concentrations mean?

In most instances, changes in electrolyte concentrations do not indicate any specific disease; they occur as secondary changes caused by certain diseases or conditions. 

• Serum calcium concentrations may become elevated from inflammation, cancer, or a condition called hyperparathyroidism. 
• Diseased kidneys may be unable to eliminate excess phosphorus and potassium through the urine, resulting in one or both electrolytes being elevated. 
• Diarrhea may cause an increased loss of sodium and bicarbonate from the gastrointestinal tract.

Occasionally, the pattern of electrolyte change may point to a specific disease. For example, a change in the ratio of sodium to potassium may suggest hypoadrenocorticism (Addison's disease) in dogs.

If electrolyte changes don't indicate the disease, why bother measuring them?

Changes in electrolyte concentrations may have significant consequences due to their role in muscle contraction, nerve conduction, and water balance. 

• Markedly elevated serum potassium concentrations can lead to cardiac arrhythmias (abnormal heartbeats). 
• Excessive loss of sodium and chloride may result in dehydration and shock. 
• A depleted phosphorus concentration in the diabetic patient may lead to red blood cell rupture and anemia.

It is important to detect changes in electrolyte concentrations so that these changes can be treated before the situation becomes severe or life-threatening. Often, electrolyte changes must be addressed first, before the underlying disease condition is controlled or treated.