Sodium (Na)
Electrolytes & minerals ·Also called: Na, sodium, serum sodium, hyponatraemia, hypernatraemia
What it is
Sodium is held within a narrow range by the kidneys and by thirst. Because water follows sodium, the concentration in blood reflects the ratio of salt to water, and both halves of that ratio can move.
Why your vet measures it
The brain is the organ most sensitive to sodium changes, and it adapts slowly. That is why a very abnormal sodium is corrected gradually rather than quickly — a rapid change can do more harm than the original abnormality. Sodium is also read alongside potassium, because their ratio is a useful pointer to Addison's disease in dogs.
What a high result can mean
- Water loss without adequate drinking — heatstroke, being shut away from water, or severe fluid loss
- Diabetes insipidus, where the kidneys cannot conserve water
- Salt ingestion, including salt dough, sea water, or paint-ball ingestion in dogs
- Loss of thirst awareness in an unwell or neurologically affected animal
What a low result can mean
- Vomiting and diarrhoea
- Hypoadrenocorticism (Addison's disease) in dogs, typically with a high potassium alongside
- Fluid collecting in the chest or abdomen
- Congestive heart failure, kidney disease, or diuretic treatment
Dogs and cats differ
Addison's disease is largely a canine condition and shows a distinctive pattern here: low sodium with high potassium, giving a sodium-to-potassium ratio below about 27. Cats develop it only rarely, so a feline low sodium points elsewhere first.
Questions worth asking your vet
- What is the sodium-to-potassium ratio?
- Could dehydration or fluid loss explain this?
- If it needs correcting, how slowly does that have to be done?
Related terms
See this value explained on your pet's own report
Upload the lab report or X-ray and get every value explained in the context of your own dog or cat — in minutes.
Explain my pet's results