Chloride in cats and dogs
Chloride is the main negatively charged ion in the fluid outside cells and travels together with sodium. On its own it says little; read next to sodium, it tells a vet whether a change is about water balance or about acid-base balance.
What it shows
According to eClinPath, chloride changes for two main reasons: gain or loss of water (with or without salts) and gain or loss of chloride-containing acids. The first moves sodium and chloride together; the second moves chloride on its own.
So the rule is simple: if sodium and chloride rise or fall in proportion, the story is about water or salt-rich fluid. If chloride moves more than sodium, the vet thinks about an acid-base disturbance — and checks bicarbonate. eClinPath recommends comparing how far each value sits from its own reference limit; some vets also calculate a “corrected chloride” that adjusts chloride for the sodium level. Small mismatches are not over-interpreted.
Higher than reference — what it may be a sign of
- Together with sodium: water loss without drinking, salt intake.
- More than sodium: loss of bicarbonate with chloride retained — for example secretory diarrhea or a kidney tubule defect (renal tubular acidosis); compensation for fast breathing (respiratory alkalosis).
- Fluids and drugs: saline and hypertonic saline; in dogs, zonisamide (an anti-seizure drug) has been reported to raise chloride.
- Artefact: bromide. The chloride electrode also reads bromide, so animals receiving potassium bromide can show falsely high chloride with normal sodium; a low anion gap is a clue.
Lower than reference
- Vomiting of stomach contents — stomach acid is rich in chloride; the Merck Veterinary Manual mentions vomiting especially after eating.
- Fluid trapped in the stomach: gastric dilatation-volvulus in dogs.
- Kidney losses: loop and thiazide diuretics, excess aldosterone.
- Compensation for a respiratory acidosis.
- Together with low sodium — the same water problems that dilute sodium.
- Artefact: marked lipemia with indirect measuring methods.
Low chloride usually comes with high bicarbonate (metabolic alkalosis); if it does not, the vet looks for a second process.
Look at together with
- Sodium — always; chloride is interpreted relative to it.
- Bicarbonate (or TCO2) — high chloride with low bicarbonate suggests one type of metabolic acidosis; low chloride with high bicarbonate, an alkalosis.
- Anion gap — calculated as (sodium + potassium) − (chloride + bicarbonate); a low value can point to bromide interference or low albumin.
- Potassium — often low as well when stomach contents are lost.
Units and conversion
Chloride is reported in mmol/L or mEq/L; for chloride the two are the same number. In the app each row keeps the unit printed on the form.
Reference range
The reference range is on your lab’s form. Chloride normally sits a little below sodium, so the numbers are not compared directly; what matters is whether both have shifted in the same direction and by a similar amount relative to their own ranges. If an animal receives bromide, tell the vet: the chloride value may be falsely high.
Cats and dogs
The sources describe no chloride pattern specific to cats: the reading is the same — next to sodium and bicarbonate. Vomiting of stomach contents lowers chloride in cats as in other small animals. VCA advises using bromides in cats with extreme caution, so the bromide artefact is mostly a dog issue.
In dogs two medicines matter for this value: VCA describes bromides as anticonvulsants used for seizures in dogs, and bromide falsely raises chloride on the analyzer; zonisamide has also been reported to raise chloride in dogs. Gastric dilatation-volvulus and vomiting from a pyloric obstruction can lower chloride and raise bicarbonate.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.