By The Pawline veterinary teamVeterinary-reviewed by Alastair Greenway, BVM&S MRCVS · 25 July 2026
Reference range · mmol/L
144160
Reference
144–160
Direction
Both unusually high and low values carry meaning.
This is the conventional reference interval. Your pet’s own report may print a slightly different range — always read the value against that. Sign in to see your pet’s value on this strip.
Sodium tracks the balance between salt and water in the body — so it's really a marker of water balance as much as salt. It shifts with hydration, kidney handling and some hormonal conditions, and both high and low values are read in that context rather than as 'too much' or 'too little' salt.
Sodium is the body's main electrolyte in the fluid outside cells, and the single most important thing to understand about it is that a sodium result is usually a story about water, not salt. The body defends its sodium concentration fiercely by moving water in and out — so when sodium is abnormal, it most often reflects a disturbance in water balance (too much or too little water relative to salt), rather than a problem with salt intake. That reframing is the key to reading it.
Sodium tracks the balance of salt and water — so an abnormal value is usually a story about water balance, read with hydration and the other electrolytes.
Reading a high result
A high sodium (hypernatraemia) usually means a water deficit — the body has lost more water than salt. Causes include inadequate water intake (a pet that can't or won't drink), excessive water loss (some kidney and hormonal conditions, severe gastrointestinal losses), and, classically, diabetes insipidus, where the body cannot conserve water. Because the concentration is defended by thirst and the kidneys, a persistent high sodium points to a genuine problem with water handling or access, and it is read with hydration status, urine concentration and the clinical picture.
Reading a low result
A low sodium (hyponatraemia) usually means a relative water excess — too much water for the salt present — or a genuine loss of sodium. Important causes include Addison's disease (hypoadrenocorticism), where the adrenal glands fail to conserve sodium (classically with a high potassium and a low sodium:potassium ratio), as well as some kidney, heart, liver and gastrointestinal conditions. A marked low sodium can affect the brain and is taken seriously; it is always interpreted alongside the other electrolytes and the clinical state.
In chronic disease
Sodium is followed as part of the electrolyte panel in conditions that disturb fluid balance — kidney, adrenal, heart and liver disease — and to guide and monitor fluid therapy. Because it moves with water balance, its trend reflects how well hydration and the underlying condition are being controlled, and sudden changes are corrected carefully (the brain adapts slowly to shifts in sodium).
Cat vs dog
Sodium is interpreted the same way in both species, with cats running slightly higher reference ranges. The water-balance framing and the differential lists apply to both. Addison's disease, a classic driver of low sodium (with high potassium), is more commonly recognised in dogs but occurs in cats too. In each, sodium is read alongside potassium, chloride and hydration.
How it's measured
Sodium is measured on a routine chemistry or electrolyte panel, in mmol/L (or mEq/L, numerically identical). It is read together with potassium, chloride and the sodium:potassium ratio, and interpreted with hydration status and urine concentration. Read the value against your own report's range.
What to do next
An abnormal sodium is a prompt to think about water balance with your vet — hydration, access to water, and conditions that disturb how the body holds or sheds water — rather than dietary salt. Read with the other electrolytes (especially potassium and the sodium:potassium ratio) and the clinical picture, it helps point towards kidney, adrenal, or fluid-balance problems and guides how they are managed.
Reference ranges reflect conventional laboratory intervals. Always interpret against your own lab's printed range and your veterinary surgeon's judgement. A brighter optimal band is shown only where a published guideline defines one, and it is cited.
This page is educational and is not a diagnosis. Lab results are interpreted in the full clinical context by your veterinary surgeon; a single value rarely tells the whole story.
