The Sodium Level Of Your Pet's Blood = Na+




Ron Hines DVM PhD

To see what normal blood and urine values are, go here

For an explanation of causes of most abnormal blood and urine tests, go here

To see how tests are grouped, go here

Sodium is the most prevalent mineral in your cat or dog's blood stream. Dry, it exists as common salt, but dissolved in the blood, it separates into its electrolyte halves, sodium (Na+ =cation) and chlorine (Cl- =anion).

In that form, most of the sodium is found in the fluid portion of your dog or cat 's blood while most of the pet’s potassium (K+ ) is found in the fluid portion of the cells of its tissues. Sodium and potassium tend to fluctuate in tandem - when sodium is high potassium is usually low and vice versa.

Levels of sodium in your dog or cat ’s blood stream are controlled by a hormone produced in its adrenal glands called aldosterone. Aldosterone alerts its kidneys of the need to conserve and reabsorb sodium from the urine as it is produced, or (by its absence) let excess sodium leave the pet’s body through its urine.

Sodium is important in keeping body fluids within your pet in their right location as well as in the proper action of its muscle and nerve cells.



Reasons Why Your Pet’s Blood Sodium Level Might Be High (hypernatremia) :

True hypernatremia (=high blood sodium) is relatively uncommon in dogs and cats.

What is common is dehydration hypernatremia (pseudohypernatremia) that increases the amount of sodium because the smaller total volume of blood has become more concentrated. However, the total amount of body sodium in that situation has not changed.

There are a lot of things that can cause dehydration. One is lack of available water. Another is over-exercise and panting. A third is heat stroke and a fourth is prolonged fever.

Loss of large amounts of body fluids through large skin wounds or burns can also elevate your pet's blood sodium in that way.

True hypernatremia can be an effect of prolonged administration of high doses of corticosteroid medications (eg prednisone) or overactive adrenal glands that produce too much similar natural cortisol (Cushing's disease/ hyperadrenocorticism).

High blood sodium levels also occur in a rare form of diabetes (diabetes insipidus). It can also occur in some forms of kidney disease and an unusual form of adrenal gland disease (hyperaldosteronism). Among other rare causes would be pets forced to drink salty water or consume highly salted food, overuse of certain laxatives (eg lactulose, sorbitol) , or overly concentrated (hypertonic) intravenous fluids. Newborn puppies and kittens can also have difficulty controlling their blood sodium levels because their kidneys are not fully developed yet. (ref)

Chronic, mild dehydration that could elevate your pet's blood sodium is thought to be most common in cats consuming dry cat foods. The signs of dehydration, as in humans, can be nebulous (vague) and only significant over time [ref1 , ref2, ref3]. More severe dehydration can accompany any disease in which apathy or reduced mobility occurs.

Reasons Why Your Pet’s Blood Sodium Level Could Be Low (hyponatremia) :

The most common cause of low blood sodium (hyponatremia) in dogs and cats is prolonged vomiting and/or diarrhea.

The second most common cause is Addison’s disease (hypoadrenocorticism) a disease of your pet's adrenal glands.

Hyponatremia can also occur in your pet when diabetes is not well controlled and the pet’s blood sugar levels remain higher than they should be. That is because high blood sugar levels can pull additional fluid out of cells ,increasing blood volume and diluting electrolytes like sodium. It does not necessarily occur because the pet's kidneys attempt to counteract that effect.

Congestive heart failure, or diuretics (eg furosemide/Lasix) used to treat it, can also cause blood sodium levels to become low. Liver disease that depresses your pet’s blood albumen levels can also cause low blood sodium levels.

Sodium can leave your pet’s blood stream and enter abnormal fluid accumulations that exist in your dog or cat. That can happen in FIP in cats, free fluid in the chest (chylothorax) pancreatitis and peritonitis. Levels can also fall temporarily after relieving urethral blockages in FUS cats.

Blood sodium levels can also be low in dogs and cats in end stage kidney failure and other health problems that cause a lower than normal blood pH (metabolic acidosis).

Fatty (lipemic) blood samples obtained too soon after a meal or in pets with other health issues (too much blood protein) can cause blood sodium levels to falsely appear low.

Contrary to what veterinarians once believed, increasing your pet's salt intake does not increase its thirst or water consumption. (ref1, ref2, email1)

Complementary Tests :

CBC/WBC and blood chemistry values, sodium/potassium ratio, ACTH stimulation test if Addison’s disease is suspected.