By The Pawline veterinary teamVeterinary-reviewed by Alastair Greenway, BVM&S MRCVS · 25 July 2026
Reference range · mmol/LDogs & cats
3.55.8
Reference
3.5–5.8
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.
Potassium is held within tight limits because both high and low levels directly affect the heart and muscles. The kidneys and adrenal glands are its main regulators, so an abnormal value points there — and a markedly high potassium, in particular, can be a medical emergency.
Potassium is the body's main inside-the-cell electrolyte, and the small amount circulating in the blood is kept within a remarkably narrow band. The reason for that tight control is stark: potassium sets the electrical excitability of nerves and muscle, and the muscle it matters most for is the heart. Both too much and too little disturb the heart's rhythm, so potassium is one of the few routine numbers that can shift from "monitor" to "emergency".
Potassium is tightly controlled because both high and low levels affect the heart and muscles. The kidneys and adrenal glands are its main regulators.
Its regulators — chiefly the kidneys and the adrenal glands — mean an abnormal potassium often points at one of those systems.
Reading a high result
A high potassium (hyperkalaemia) is potentially dangerous because, at marked levels, it slows and destabilises the heart's rhythm and can be life-threatening. Important causes include:
Urinary obstruction — a blocked cat that cannot pass urine builds up potassium rapidly; this is a true emergency.
Kidney failure (especially acute) and Addison's disease (hypoadrenocorticism), where the adrenal glands fail to help excrete potassium — classically with a low sodium:potassium ratio.
Severe tissue damage and certain other conditions.
There is also a frequent false positive: potassium leaking out of blood cells after the sample is taken (haemolysis, delayed processing, or — in some breeds like the Akita — high-potassium red cells) can raise the measured value without the pet being affected. So a high potassium in a well animal is often rechecked on a clean, promptly-processed sample, while a high potassium in an unwell one (a blocked cat, a collapsed dog) is treated as real and urgent.
Reading a low result
A low potassium (hypokalaemia) causes muscle weakness — a classic sign in cats is a ventroflexed (drooping) neck, unable to hold the head up. Causes include chronic kidney disease (a common driver in cats), losses from vomiting or diarrhoea, and certain hormonal conditions. When marked, low potassium also affects the heart and is corrected deliberately.
In chronic disease
Potassium is tracked in chronic kidney disease (where cats in particular tend to run low and may need supplementation), in Addisonian patients on treatment, and whenever medicines that affect potassium are used. Following it over time keeps it within the safe band as the underlying condition and its treatment evolve.
Cat vs dog
Potassium is interpreted the same way in both species, but two feline scenarios stand out: the blocked male cat with dangerous hyperkalaemia, an emergency, and the chronic kidney disease cat who trends towards hypokalaemia and neck weakness. In dogs, a low sodium:potassium ratio driving a high potassium classically raises Addison's disease. In both, the sample must be handled cleanly, because artefactual highs are common.
How it's measured
Potassium is measured on a routine chemistry or electrolyte panel, in mmol/L (or mEq/L, numerically the same). Prompt, clean sample handling is essential to avoid falsely high values from cells leaking potassium. It is read alongside sodium and the sodium:potassium ratio, which adds specific diagnostic value. Read the value against your own report's range.
What to do next
A markedly high potassium in an unwell pet — above all a cat that may be blocked — needs urgent veterinary attention, because of the risk to the heart. A high potassium in a well pet is often rechecked on a clean sample first. A low potassium is corrected and its cause (often kidney disease in cats) pursued. Because potassium sits so close to the heart, both extremes are taken seriously.
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.
