Ron Hines DVM PhD
Your Pet’s Resting Blood Cortisol Level
Veterinarians attempt to measure cortisol levels when your pet is at ease or “resting” as opposed to when it is active or excited. That is because any exertion (physical or mental) will raise blood cortisol levels. Even with that caution, single blood cortisol determinations are not of much value because levels fluctuate so much. A better way to judge your pet’s adrenal gland function is with the ACTH stimulation test or dexamethasone suppression test or perhaps your dog or cat’s urine cortisol:creatinine ratio.
Cortisol is an adrenal hormone with a great number of effects on your pet’s body. Its level in normal pets goes up or down quickly in response to stress. The corticosteroid medications (like prednisone) that veterinarians administer copy or mimic the action of your pet’s natural cortisol. Too much cortisol (Cushing’s Disease) or too little cortisol (Addison’s Disease) result from a cortisol imbalance.
Your pet’s resting cortisol level is not very useful in diagnosing Cushing’s disease. Many Cushing’s dogs have normal resting values. But a normal result does make a diagnosis of Addison’s disease unlikely.
Determining your pet’s resting or unstimulated level of cortisol is not very helpful, in itself, in diagnosing either of those conditions because it is continuously fluctuating (changing) to meet the pet’s current needs. But it gives your veterinarian a baseline from which to judge how well your pet’s adrenal glands are working when subjected to stress.
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