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Hyponatremia is the clinical term given to a condition in which a dog is suffering from low concentrations of serum sodium in the blood. As a component of the extracellular fluid (fluids outside of the cells), sodium is the most abundant positive charged atom in the body. For this reason, a condition of hyponatremia usually reflects a concurrent condition of hyposmolality, an underconcentration of osmotic solution in the blood serum; that is, a lack in the ability of body fluids to pass through the cellular membranes (osmosis), by which the body's chemical concentrations are kept in balance. Hyposmolality is typically associated with a decreased amount of sodium content throughout the body.
Theoretically, hyponatremia can be caused by either water retention or solute loss (loss of a dissolvable body substance -- in this case, salt/sodium is the solute). Most solute loss occurs in iso-osmotic solutions (e.g., vomit and diarrhea), and as a result, water retention in relation to solute is the underlying cause in almost all patients that are diagnosed with hyponatremia. In general, hyponatremia occurs only when there is a defect in the kidney's ability to excrete water.
Normal osmolar hyponatremia, causes with typical concurrent conditions:
Hyperglycemia – excessive glucose/sugar in the blood
Primary polydipsia – excessive thirst
Congestive heart failure (CHF)
A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. If your dog has hyponatremia, these tests will confirm low serum sodium concentration. Other disorders that can mimic hyponatremia, and which will need to be excluded, are hyperglycemia, hyperproteinemia, and hyperlipidemia.
Your veterinarian may also recommend testing the serum osmolality will be tested. The osmolality balance of your dog's urine will be indicative of the kidney's ability to excrete water, and the sodium concentration found in the urine may indicate a low volume of circulating sodium.
A medical condition involving excessive thirst
An in-depth examination of the properties of urine; used to determine the presence or absence of illness
The amount of pressure required to cause osmosis to stop
A condition of the blood in which the fat levels are high
Elevated levels of glucose in the blood
Anything that causes excessive urination
The transfer of water through a type of membrane