Ron Hines DVM PhD
The Cortisol:Creatinine Ratio Of Your Pet’s Urine (= UC:Cr Index)
The cortisol-to-creatinine ratio of your dog or cat’s urine (its first void of the morning – obtained at home and brought to your veterinarian) gives your vet considerably more information than a single resting blood cortisol level determination regarding the condition of your pet’s adrenal gland and the pituitary gland on which adrenal glands rely on for instructions. This test is most commonly used as an initial screening test for Cushing’s disease.
Whereas your dog or cat’s blood levels of cortisol fluctuate during the day, its urine cortisol levels are more constant ( having had time to accumulate). However the varying concentration of your pet’s urine during the day make urine cortisol values difficult for your veterinarian to interpret. It would take many determinations throughout the day to be of much help. The concentration or specific gravity of your pet’s urine varies depending on the amount of water it drinks and the activity of its kidneys. A low urine cortisol level could just mean you pet recently consumed water. A high urine cortisol level could mean your pet encountered stress or exertion. 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 obtained.
Although this test is not nearly as accurate as the ACTH stimulation test or Dexamethasone suppression test in judging your pet’s adrenal gland function, it is a simple, non-invasive (no needle), lower cost initial screening test for adrenal gland problems like Cushing’s disease When the test is normal, Cushing’s disease is unlikely to be your pet’s problem. But when the results are elevated, there are other stress-related and non-adrenal gland diseases that could account for it. In those cases, an ACTH stimulation or Dexamethasone suppression test will still have to be performed to confirm that the initial UC:Cr results were meaningful. The UC:Cr test or index can also be used as an initial screening test to help rule out Addison’s Disease (the reverse problem as Cushing’s Disease = too little cortisol) although that use of the test is considerably less frequent.
What Conditions Could Cause My Pet’s Cortisol:Creatinine ratio to be elevated?
This test is only a preliminary screening test for Cushing’s disease. When it is normal, the dog probably does not have typical Cushing’s. When it is elevated, less than half of the pets have typical Cushing’s disease. They will need an ACTH test or a dexamethasone suppression test to know for sure. When signs of Cushing’s disease are present but the cortisol:creatinine test is normal, it is wise to screen them for what is called “atypical” Cushing’s disease. (read here)
False-positive elevations can be due to diseases of the stomach/intestinal, kidney, lower urinary tract, liver, neurologic, immune-mediated diseases or congestive heart failure.
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