Endogenous ACTH in cats and dogs

ACTH is the pituitary hormone that tells the adrenal glands to make cortisol. “Endogenous” means the body’s own ACTH, not the synthetic ACTH injected in a stimulation test. Vets usually measure it after the diagnosis is already made, to find out where the problem sits — in the pituitary or in the adrenal glands. The hormone breaks down quickly in a tube, so how the sample is taken and shipped matters as much as the number.

SectionHormones
SampleBlood (EDTA plasma) — chilled straight away, plasma separated quickly and frozen; usually sent to an external laboratory
Unitspmol/L · 1 pg/mL = 0.2202 pmol/L
On formseACTH

What it shows

The pituitary releases ACTH, ACTH drives the adrenal glands to make cortisol, and cortisol in turn tells the pituitary to slow down. Measuring ACTH shows which part of this loop is out of order.

  • Too much cortisol (Cushing’s, hyperadrenocorticism). If the cause is in the pituitary, ACTH stays within the range or goes up. If the cause is a cortisol-producing tumour of an adrenal gland, high cortisol switches the pituitary off and ACTH is very low or undetectable.
  • Too little cortisol (Addison’s, hypoadrenocorticism). If the adrenal glands themselves are destroyed (primary disease), the pituitary pushes hard and ACTH is high. If the pituitary does not send enough ACTH (secondary disease), ACTH is low.

So ACTH does not diagnose either disease on its own — that is done with cortisol tests. It answers the next question: where is the problem.

Higher than reference — what it may be a sign of

  • Pituitary-dependent Cushing’s — in a dog with confirmed hyperadrenocorticism, ACTH within the range or above it points to the pituitary form.
  • Primary Addison’s disease — an increased ACTH in an animal not yet receiving hormone replacement supports destruction of the adrenal glands themselves.
  • A result in the grey zone — some ACTH values are inconclusive and do not clearly fall on either side; the vet then relies on other tests.

Lower than reference

  • Adrenal tumour as the cause of Cushing’s — in confirmed hyperadrenocorticism, low to undetectable ACTH points to a cortisol-producing adrenal tumour.
  • Secondary Addison’s disease — in an animal with known Addison’s disease, low ACTH points to a pituitary cause; this form is rare.
  • A sample that waited too long or warmed up — ACTH breaks down in blood outside the body, so a falsely low result is possible if the sample was not chilled, separated and frozen in time.

Look at together with

  • Cortisol in ACTH stimulation or dexamethasone tests — these confirm Cushing’s or Addison’s; endogenous ACTH comes after.
  • Urine cortisol : creatinine ratio — a screening test.
  • Sodium and potassium — in Addison’s disease the lack of aldosterone shifts them; together with aldosterone they help separate primary from secondary disease.

Units and conversion

ACTH is reported in pmol/L or in pg/mL. One pg/mL is about 0.22 pmol/L, so 20 pg/mL is roughly 4.4 pmol/L, and 1 pmol/L is about 4.5 pg/mL. The app keeps the unit printed on the form and converts for the chart. Laboratories do change ACTH methods: one veterinary lab switched to a new method in 2021, began reporting in pg/mL and updated its reference ranges — so an older result or one from another lab is compared with care.

Reference range

The reference range is on your lab’s form. It depends on the laboratory and the method, and for ACTH the form often carries a comment on how the lab reads values in suspected Cushing’s or Addison’s disease. The hormone is fragile: the sample must be chilled at once and the plasma separated quickly; if this was not done, the lab may ask for a repeat sample. A protease inhibitor (aprotinin) added to the EDTA tube slows the breakdown, and such a sample keeps for up to 4 days below 4 °C.

Cats and dogs

Cats

Cushing’s disease is quite rare in cats, mostly in middle-aged and older cats, and almost 80% of affected cats also have diabetes. As in dogs, the pituitary form is more common, and once the disease is confirmed, a low or undetectable ACTH suggests an adrenal tumour. In a cat not yet on hormone replacement, an increased ACTH supports primary Addison’s disease, which in cats is uncommon.

Dogs

In dogs with Cushing’s, about 85% have the pituitary form and about 15% an adrenal tumour, which is why telling them apart matters. Addison’s disease is seen mostly in dogs, and most cases are primary adrenal failure, where ACTH is expected to be high. For dog plasma, labs ask for plastic tubes and fast separation.

In the app

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.

Open the app

Sources

  1. Greco DS. Cushing Disease (Pituitary-Dependent Hyperadrenocorticism) in Animals. Merck Veterinary Manual, professional version, September 2024.
  2. Van Vertloo L. Addison Disease (Hypoadrenocorticism) in Animals. Merck Veterinary Manual, professional version, July 2024.
  3. Michigan State University Veterinary Diagnostic Laboratory. Adrenal Testing in Dogs.
  4. Michigan State University Veterinary Diagnostic Laboratory. Adrenal Testing in Cats.
  5. Cornell University Animal Health Diagnostic Center. Endocrinology Submission Guidelines.
  6. Michigan State University Veterinary Diagnostic Laboratory. Assay Transition for Endogenous ACTH (news, 2021).

Updated 6 November 2026 · Mihail Ivanov, creator of Pet Tracker Space · Written with Claude and checked against the sources above.

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.