Hyponatremia is defined as a blood sodium level <135 mEq/L (normal is 140 - 165).
Body stores of sodium and potassium are intimately related and maintained by balanced intake and excretion, intracellular and extracellular osmotic pressure, and pH. Hyonatremia is commonly associated with hyperkalemia.
Sodium-potassium (Na:K) ratio has frequently been used as a diagnostic tool to identify adrenal insufficiency.
The normal Na:K ratios in dogs range from 27:1 to 40:1, while the values in canine hypoadrenocorticism (Addison’s disease) are often below 27:1 and may be below 20:1 in primary hypoadrenocorticism, characterized by hyponatremia, hypochloremia and hyperkalemia.
Other disorders which can cause hyponatremia include:
- Dietary deficiencies of calcium and phosphorus
- Inflammatory diseases resulting in intracellular sodium compartmentalization - pancreatitis, septicemia, neoplasia
- Infections resulting in sodium sequestration - bacterial pneumonia, pyometra, abscess, pyoderma
- Fluid loss - chronic renal disease, diabetes mellitus, peritoneal/pleural effusion, congestive heart failure
- Inappropriate antidiuretic hormone secretion - hepatitis, hydrocephalus
- Intestinal electrolyte loss due to vomiting or diarrhea, resulting in metabolic alkalosis, hypokalemia and hyponatremia - canine parvovirus, parasites, gastritis, gastric dilation and volvulus, inflammatory bowel disease, intestinal foreign body obstruction
- Artefactual - laboratory error
Clinically affected dogs present with dehydration, lethargy, myalgia, cramping and reluctance to walk.
Parenteral electrolyte replacements are usually sufficient to correct hyponatremia.
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