Why Is My Dog Or Cat’s Urine Cortisol:Creatinine Ratio High Or Low?
Ron Hines DVM PhD
The Cortisol:Creatinine Ratio Of Your Pet’s Urine (= UC:Cr Index)
Obtaining meaningful results regarding your dog or cat’s body cortisol level is a challenge for your veterinarian. That is because the amount of cortisol in your pet’s system varies from hour to hour and minute to minute depending on the pet’s level of stress, anxiety and exertion. A simple trip to your veterinarian’s office is likely to affect the results. It would take many blood cortisol determinations throughout the day to be of much help – if any. However, the urine in your pet’s bladder accumulated over a much longer period of time. Your pet’s urine also contains small amounts of cortisol that can be measured. The concentration (specific gravity) of your pet’s urine varies depending on the amount of water it drank and the activity of its kidneys, so just measuring its cortisol content does not tell you much. A low urine cortisol level could just mean your pet recently consumed water. A high urine cortisol level could just mean your pet was a bit dehydrated. Creatinine, however, is released into your pet’s urine at a much steadier rate. So by comparing the concentration of one to the other, your veterinarian can make more sense of the data he/she obtained.
When one measures the amount of both compounds in your pet’s urine and divides the cortisol number by the urine creatinine number, the ratio represents a more accurate indication of its body cortisol level over longer periods of time. The best sample to bring to your veterinarian is your dog or cat’s first void of the morning – obtained at home and brought to your veterinarian. That will gives your vet considerably more information than a single resting blood cortisol level determination regarding the condition of your pet’s adrenal glands and its pituitary gland on which the adrenal glands rely on for instructions as to how much cortisol to produce.
Adrenal gland/cortisol problems appear to be considerably more common in dogs than in cats. But that might just be because we have not been looking for them or know what the symptoms of low or high cortisol levels in cats might be. (read here)
What Conditions Could Cause My Pet’s Cortisol:Creatinine ratio to be High?
The UC:Cr test is most commonly used as an initial screening test for dogs when Cushing’s disease, (aka hypercortisolism or hypercortisolemia) is suspected. The UC:Cr test is simple to run. However, it is best relied upon only as an initial screening test. That is because it is a test with high sensitivity but low specificity. That means that it is likely to identify most dogs and cats that are candidates for having Cushing’s disease. But it is so sensitive that it will pick up a considerable number of pets that do not have Cushing’s disease (false positives). However, if your dog or cat has normal UC:Cr test results, Cushing’s disease is probably not its health issue. To be sure that your pet actually has Cushing’s disease, one of two test with higher specificity must then be run. That test is either the ACTH stimulation test or the Dexamethasone suppression test. Both of those two tests are the opposite of UC:Cr, they have high specificity but lower sensitivity for blood cortisol issues. They are more time-consuming, stressful and expensive to run. So, it is more economical and less stressful to run the UC:Cr test first to weed out (eliminate) the pets that probably do not need one of the other two tests.
Your pet’s adrenal glands produce a variety of hormones besides cortisol. When typical signs of Cushing’s disease are present, but the ACTH stimulation test or the Dexamethasone suppression test results are normal, it might be wise to screen them for what is called “atypical” Cushing’s disease. (read here) Others including myself believe that when adrenal glands malfunction in ways that do not increase cortisol, veterinarians need to give it a different name. (read here)
What Conditions Could Cause My Pet’s Cortisol:Creatinine ratio to be Low?
The UC:Cr test or index can also be used as an initial screening test to help rule out Addison’s Disease. Addison’s disease is the reverse problem from Cushing’s Disease/=hypoadrenocorticism or too little cortisol and aldosterone. The use of the test for that purpose is considerably less frequently used by veterinarians, but it’s frequent for this use may increase. Recent research indicates that the urine cortisol:creatinine test is a good initial screening test for an adrenal gland disease. As with its more frequent use to detect high cortisol issues, it has good sensitivity but poor specificity for detecting low cortisol issues. (read here)
Those pets with suspected insufficient cortisol production also need a confirmatory ACTH or Dexamethasone suppression test. However, some feel that these tests are less able to diagnose Addison’s Disease (low cortisol) than Cushing’s Disease (high cortisol). (read here)
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