By The Pawline veterinary teamVeterinary-reviewed by Alastair Greenway, BVM&S MRCVS · 25 July 2026
Reference range · ratioDogs & cats
2740
Reference
27–40
Direction
Lower values are the concern.
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.
The sodium-to-potassium ratio is a derived value that acts as a screening flag: a low ratio (classically under 27) is the recognised prompt to consider Addison's disease. It's a red flag to investigate, not a target to optimise.
The Na:K ratio simply divides sodium by potassium. What makes this bit of arithmetic clinically famous is a single pattern: in Addison's disease (hypoadrenocorticism), the adrenal glands fail to help the body hold onto sodium and excrete potassium — so sodium falls and potassium rises together, and their ratio drops sharply. Because both numbers move in the same telling direction, the ratio amplifies a signal that either alone might understate. It is, in effect, a screening flag rather than a value to manage.
The Na:K ratio is a screening flag: a low ratio (classically under 27) is the recognised prompt to consider Addison's disease.
Reading a low ratio
A low Na:K ratio — classically below about 27, and more strikingly below 20 — is the recognised prompt to consider Addison's disease, especially in a young-to-middle-aged dog with vague, waxing-and-waning illness (poor appetite, lethargy, vomiting, sometimes collapse). It is a screening trigger: a low ratio doesn't diagnose Addison's by itself, but it says "test for it" — usually with an ACTH stimulation test, the definitive step.
Crucially, a low ratio has other causes too, and these must be considered so Addison's isn't the only thought: severe gastrointestinal disease (some whipworm infections are notorious mimics), certain kidney and urinary problems (including a blocked or ruptured bladder), some effusions, and — importantly — the artefactual high potassium from a poorly-handled sample (haemolysis, delayed processing, or high-potassium red cells in certain breeds), which drops the ratio without any real disease. So a low ratio on a well pet is often rechecked on a clean sample before it is believed.
Reading a high or normal ratio
A normal ratio is reassuring against the Addison's pattern. A high ratio is not a recognised concern in its own right and simply reflects the sodium and potassium values that produced it. Because the ratio's whole purpose is to flag the low pattern, the high and normal ends carry little independent meaning.
In chronic disease
The Na:K ratio is a screening and monitoring aid rather than a target. In a diagnosed Addisonian on treatment, sodium and potassium (and hence the ratio) are followed to confirm the electrolytes are being kept in the normal range. Otherwise, the ratio's role is simply to catch the classic low pattern whenever it appears, prompting the specific work-up.
Cat vs dog
The ratio is interpreted the same way in both species, using the same rough cut-offs. Addison's disease, the headline reason to notice a low ratio, is more commonly recognised in dogs but does occur in cats. In both species, the same list of non-Addisonian causes — gut disease, urinary problems, and sample artefact — must be weighed, and a low ratio in a well animal is confirmed on a clean sample.
How it's measured
The Na:K ratio is calculated from the measured sodium and potassium on a chemistry or electrolyte panel; it is a ratio and carries no unit. Because it depends on potassium, which is easily raised by poor sample handling, clean and prompt collection is essential. Read the value against your own report's range, and treat a low ratio as a flag to confirm and investigate.
What to do next
A low Na:K ratio is a prompt to consider Addison's disease and to test for it (an ACTH stimulation test), while also weighing the other causes — gastrointestinal or urinary disease — and ruling out a sample artefact by rechecking a clean sample. As a derived screening flag, it is acted on by investigation, not by trying to adjust the number itself.
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.
