Urine cortisol : creatinine ratio (UCCR) in cats and dogs

What it shows

Cortisol is a hormone of the adrenal glands; its production rises with stress and illness. Cortisol in urine reflects the average blood cortisol over the time the urine was forming (VCA). The raw number is distorted by how concentrated the urine is: the same animal will show more cortisol per litre in concentrated urine than in dilute urine. Creatinine leaves the body in urine at a fairly steady rate, so dividing cortisol by creatinine corrects for concentration (VCA).

That is why a form may show two lines. Urine cortisol on its own is hard to interpret, because it moves with urine concentration. The UCCR is the corrected figure vets actually use. Merck describes it as highly sensitive for separating healthy dogs from dogs with hyperadrenocorticism, but not highly specific.

Higher than reference — what it may be a sign of

• Cushing’s syndrome (hyperadrenocorticism) — a raised ratio is typical, but on its own it is not diagnostic (VCA).
• Stress — even a car ride or a clinic visit can raise the ratio (VCA); Merck mentions stress from transport and from cystocentesis.
• Other illnesses — moderate to severe illness unrelated to the adrenal glands can raise it (Merck, VCA).
• A lot of blood in the urine and recent corticosteroid medicines (VCA).

A raised result is followed by other tests only when signs and screening tests also fit — Merck names the ACTH stimulation test and dexamethasone suppression tests.

Lower than reference

A result within the range is the main reason to run this test: VCA notes that a normal ratio makes Cushing’s syndrome unlikely, although it is still read together with the rest of the clinical picture. The sources describe no separate disease that a low UCCR points to.

Look at together with

• Clinical signs — increased drinking and urination, appetite, coat and skin; the test is chosen because of them.
• Routine bloodwork and urinalysis — VCA advises further testing when a complete blood count, biochemistry and urinalysis support the suspicion.
• Urine specific gravity — dogs with Cushing’s syndrome usually have dilute urine (VCA, Merck).
• Urine glucose and blood glucose — diabetes accompanies Cushing’s in some dogs and many cats (VCA).
• Urine culture — Merck notes that many dogs with hyperadrenocorticism have a urinary tract infection, often without inflammatory cells in the sediment.

Units and conversion

Cortisol and creatinine are both measured in the urine and divided. Creatinine is present in far greater amounts, so the ratio is a very small number, and labs print it scaled — the form shows it with the unit ×10⁻⁶. Urine cortisol on its own is reported in nmol/L. The two are different quantities and cannot be converted into each other; there is also no conversion for blood creatinine here, because only urine values are used. Ranges depend on the laboratory’s method, so compare the result with the range printed next to it.

Reference range

The reference range is on your lab’s form. How the urine is collected matters as much as the number. VCA recommends a single first-morning sample collected at home to avoid the stress of a hospital visit; Merck also prefers free-catch urine collected by the owner at home. The sample is usually sent to a reference laboratory. In one longer protocol described by Merck, urine is collected on several mornings in a row, before and after dexamethasone is given — the vet explains the plan if it is needed.

Cats and dogs

Sources

1. VCA Animal Hospitals — Urine Cortisol
2. Greco DS. Cushing Disease (Pituitary-Dependent Hyperadrenocorticism) in Animals. Merck Veterinary Manual
3. VCA Animal Hospitals — Cushing's Disease: Testing
4. VCA Animal Hospitals — Cushing's Disease in Cats