At the 2026 VMX Conference in Orlando, Florida, I had the opportunity to sit in on an outstanding endocrinology presentation by two of my amazing colleagues, Patty Lathan, VMD, DACVIM (SAIM) and Bill Saxon, DVM, DACVIM (SAIM), DACVECC. One discussion point clearly captured the room’s attention: what dose of cosyntropin should we use to screen dogs for hypoadrenocorticism (Addison’s disease)?
When the speakers recommended 1 µg/kg instead of the traditionally taught 5 µg/kg dose, the audience response was immediate and telling. Many clinicians were unfamiliar with this evidence-based approach. That moment underscored the need to share this information more broadly, especially given its diagnostic validity and its economic advantages for pet owners.
Addison’s Disease in Dogs: A Brief Clinical Context
Hypoadrenocorticism remains one of the great diagnostic mimics in small-animal medicine. Dogs may present with vague, waxing-and-waning clinical signs such as lethargy, gastrointestinal upset, weight loss, or episodic collapse. Laboratory abnormalities (e.g., hyponatremia, hyperkalemia, hypoglycemia, azotemia, or anemia) raise suspicion, but definitive diagnosis requires ACTH stimulation testing.
Cosyntropin (synthetic ACTH) directly evaluates adrenal cortisol reserve and remains the gold standard diagnostic test.
Traditional Teaching vs. Current Evidence
For years, veterinary curricula and reference texts taught a cosyntropin dose of 5 µg/kg IV for ACTH stimulation testing. While effective, this approach is not the most efficient or cost-conscious option.
What Changed?
A pivotal study published in Journal of Veterinary Internal Medicine demonstrated 1 µg/kg of cosyntropin produces equivalent diagnostic discrimination between dogs with normal adrenal function and those with hypoadrenocorticism when compared with the higher 5 µg/kg dose (PMID: 30230611).
Importantly:
- Peak cortisol responses remained diagnostically reliable
- Dogs with Addison’s disease showed inadequate cortisol responses at both doses
- No clinically meaningful loss of sensitivity or specificity occurred with the lower dose
Why 1 µg/kg Makes Clinical Sense
1. Diagnostic Accuracy Is Preserved
Low-dose cosyntropin reliably stimulates the adrenal cortex in dogs with functional adrenal tissue. Dogs with primary hypoadrenocorticism still fail to mount an appropriate cortisol response, allowing accurate diagnosis.
2. Lower Cost Improves Access to Care
Cosyntropin is expensive, particularly for medium- to large-breed dogs. Using one-fifth the dose substantially reduces test cost, making definitive endocrine testing more accessible for clients and reducing delays in diagnosis.
3. Better Resource Stewardship
Reduced dosing minimizes drug waste, improves vial utilization in multi-patient practices, and aligns with broader goals of cost-effective, evidence-based medicine.
Practical Implementation in Clinical Practice
Recommended Protocol
- Dose: Cosyntropin 1 µg/kg IV
- Baseline cortisol: Collected immediately prior to administration
- Post-ACTH cortisol: Collected 60 minutes after injection
Interpretation
- Normal dog: Adequate post-ACTH cortisol response
- Hypoadrenocorticism: Minimal or absent cortisol response (result <2 ug/dL or <55 nmol/L)
The interpretive cutoffs remain unchanged from traditional testing protocols.
Take-Home Message for Clinicians
The recommendation to use 1 µg/kg of cosyntropin for ACTH stimulation testing in dogs is not a shortcut; it is a data-driven refinement of best practice. This approach maintains diagnostic accuracy, reduces financial burden for clients, and reflects thoughtful stewardship of veterinary resources.
If you have continued to default to 5 µg/kg simply because “that’s how it’s always been done,” now is the time to update your protocol. Sometimes progress in medicine does not require new technology, just the willingness to apply the evidence already in front of us.
