What is the urine cortisol/creatinine ratio?
Cortisol is a stress hormone that is excreted from the body in urine. The amount of cortisol in the urine reflects the average cortisol concentration in the blood at the time the urine was formed. However, this measurement is affected by the urine’s concentration.
Creatinine is a product of muscle metabolism, and it is normally lost in the urine at a relatively steady rate. For that reason, the ratio of cortisol to creatinine in the urine can be used to more accurately assess if there is an abnormal amount of cortisol in the body without being affected by the concentration of the urine.
Why is this test done?
The urine cortisol/creatinine ratio is usually evaluated in animals suspected of having Cushing's disease (also known as hyperadrenocorticism). An animal with Cushing’s disease produces an excessive amount of cortisol. This increased blood cortisol results in increased loss of cortisol into the urine. Therefore, the urinary cortisol/creatinine ratio is usually increased in animals with Cushing's disease. See handout “Cushing’s Disease in Dogs” for more information.
Does an increased urine cortisol/creatinine ratio always mean that Cushing's disease is present?
No, a high urine cortisol/creatinine ratio does not always mean an animal has Cushing’s disease. There are other causes of an increased urinary cortisol/creatinine ratio.
- Simple stress, such as a car ride or a visit to your veterinarian, may cause a mild increase in the ratio.
- The presence of other illnesses may result in increased cortisol production by the adrenal glands.
- Significant blood in the urine or recent use of corticosteroids can cause this ratio to increase.
However, if other initial screening tests (CBC, urinalysis, and biochemical profile) are supportive of Cushing's disease, and your pet has relevant clinical signs, then further testing for Cushing's disease is indicated. Additional tests may include the ACTH stimulation test and/or the dexamethasone suppression test.
What does a normal urine cortisol/creatinine ratio mean?
Like any other test, the urine cortisol/creatinine ratio result must always be evaluated along with other clinical information and data. However, if the cortisol/creatinine ratio is normal (not elevated), then it is unlikely your pet has Cushing's disease.
How is the urine cortisol/creatinine ratio test done?
To do the cortisol/creatinine ratio test, you will collect a single urine sample, first thing in the morning. Ideally, this sample should be collected at your home, to minimize the effects of stress due to a hospital visit. By collecting a first morning sample, the average amount of cortisol that has been lost into the urine overnight can be assessed. The urine sample is usually sent to a referral laboratory for analysis.
