Aldosterone in cats and dogs: baseline and after ACTH stimulation
Aldosterone is the adrenal hormone that keeps sodium and water in the body and gets rid of potassium. In cats it is measured mainly when low potassium or high blood pressure raises the question of an adrenal gland making too much of it. In dogs it is measured mostly in suspected Addison’s disease, sometimes before and after an ACTH injection.
What it shows
The outer layer of the adrenal glands makes aldosterone. It acts on the kidneys: sodium and water are kept, potassium is passed into the urine. Its release is driven by the renin–angiotensin system, which responds to blood volume and blood pressure, and directly by potassium in the blood. So in a healthy animal low potassium goes with low aldosterone, and an animal that has lost fluid may have a high one for a good reason.
On a form there may be two lines:
- Aldosterone — a baseline sample at rest, without any stimulation. In cats this is usually enough to look for excess aldosterone.
- Aldosterone post-ACTH — the sample taken after the vet has injected synthetic ACTH, during the ACTH stimulation test. It shows whether the adrenal glands can produce aldosterone when stimulated. Read together with the baseline value, it is useful when cortisol results are blurred by recent steroid medicines, because those medicines affect aldosterone production only a little.
Higher than reference — what it may be a sign of
- Primary hyperaldosteronism in cats — the adrenal gland makes aldosterone on its own, ignoring the body’s signals. Most recognised cases come from an adrenal tumour; some cats have enlargement of the aldosterone-producing layer on both sides. Potassium is lost, which causes weakness, and sodium and water retention can raise blood pressure.
- A value inside the range can also be “too high” — when potassium is low, aldosterone is expected to be suppressed, so a value within or above the range at that moment is inappropriate.
- Secondary rise — aldosterone also goes up as a normal answer of the renin–angiotensin system. A high value alone does not tell primary from secondary causes; vets look at renin, if available, and at the whole picture.
Lower than reference
Low or undetectable aldosterone, at baseline and after ACTH, fits primary Addison’s disease, where the adrenal glands themselves are destroyed. Electrolytes can still be within the range despite low aldosterone, so normal sodium and potassium do not rule it out. In forms where only cortisol is lacking — the so-called atypical Addison’s disease, or a cause in the pituitary — aldosterone may be preserved, and this is how the test helps tell the forms apart. Atypical disease can later progress to a lack of aldosterone too.
Look at together with
- Potassium and sodium — aldosterone is read against them; low potassium with unsuppressed aldosterone is the key pattern in cats.
- Blood pressure and an eye check — high pressure can damage the retina.
- Creatinine — chronic kidney disease also causes high pressure and low potassium, and affected cats can have both conditions.
- Cortisol and endogenous ACTH — in suspected Addison’s disease.
Units and conversion
Aldosterone is reported in pmol/L or in pg/mL. One pg/mL is about 2.77 pmol/L, so 100 pg/mL is roughly 277 pmol/L, and 1000 pmol/L is about 360 pg/mL. The baseline and post-ACTH lines use the same units. The app keeps the unit printed on the form and converts for the chart.
Reference range
The reference range is on your lab’s form, and the post-ACTH value has its own interval or comment from the lab. Aldosterone is always read against potassium, sodium, blood pressure and kidney function at the same moment. As a guide, the Michigan State University laboratory notes that cats with aldosterone-secreting adrenal tumours often have baseline values above 1000 pmol/L; it gives no single cut-off for other causes. When renin can be measured too, the aldosterone-to-renin ratio is considered the most reliable test, but it is not routinely available for cats.
Cats and dogs
Primary hyperaldosteronism is a disease of middle-aged and older cats, without a known breed or sex link. Lethargy and weakness are the most common signs; severe low potassium can make a cat hold its head bent down towards the chest or walk on its hocks. Because kidney disease also causes high pressure and low potassium, the adrenal cause can be overlooked.
In dogs aldosterone is measured mainly in suspected Addison’s disease, which is seen most often in dogs. A sodium-to-potassium ratio below 27 suggests Addison’s disease but does not prove it, and aldosterone helps where electrolytes are normal or cortisol is confused by earlier steroid medicines.
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
- Van Vertloo L. Feline Primary Hyperaldosteronism. Merck Veterinary Manual, professional version, July 2024 (updated May 2025).
- Van Vertloo L. Addison Disease (Hypoadrenocorticism) in Animals. Merck Veterinary Manual, professional version, July 2024.
- Michigan State University Veterinary Diagnostic Laboratory. Adrenal Testing in Cats.
- Michigan State University Veterinary Diagnostic Laboratory. Adrenal Testing in Dogs.
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.