Screening and Diagnostic Testing for Cushing's Disease

Overview

There are a number of screening and diagnostic tests that can be run to help determine whether your pet has Cushing’s disease. There are also other tests that can help determine the cause of the Cushing’s disease: pituitary or adrenal. Most small breed dogs have the pituitary form (i.e no adrenal tumour).

For the blood tests that require a stay in the hospital, it is preferable that your pet is fasted overnight – continue access to water but offer no food after 8 pm. Please also try to avoid overexcitement or stress prior to dropping off. Some people prefer to bring the pet back at the scheduled times to reduce stress.

Screening tests

A number of screening tests, both blood and urine tests can be useful in the diagnosis of Cushing’s disease. 

Complete blood count (CBC)

Red blood cell, white blood cell and platelet count.

An increase in white blood cells can indicate Cushing’s disease due to excess cortisol or underlying inflammation.

Biochemistry

An indication of liver, kidney and pancreas function

An increase in blood glucose, liver enzymes, blood lipid and cholesterol can indicate Cushing’s disease.

Urinalysis

Diluted urine can indicate an increase in the consumption of water, which can occur in Cushing’s disease.

An infection can also occur in dogs with Cushing’s disease.

The presence of glucose in the urine can indicate concurrent diabetes.

 

Diagnostic blood tests

Endogenous ACTH assay A blood test used to help differentiate between pituitary-related Cushing’s disease and adrenal-related Cushing’s disease. An increased endogenous ACTH may indicate a pituitary-related Cushing’s disease. A normal endogenous ACTH does not rule out pituitary-related Cushing’s disease. NOT ROUTINELY USED
ACTH stimulation test This blood test is run in the hospital and requires 2 blood samples. ACTH is a hormone produced by the pituitary gland in the brain. When cortisol increases, ACTH levels drop. The ACTH stimulation test checks the pet’s adrenal glands to produce cortisol following an injection of synthetic ACTH. The first blood sample is taken before the injection and the 2nd blood sample is taken 2 hours after the injection. An exaggerated increase of cortisol following the injection is found in pets with Cushing’s disease. THIS IS USUALLY THE TEST WE USE TO ASSESS RESPONSE TO THE TREATMENT, IT IS SOMETIMES USED AS AN INITIAL TEST AS WELL.
Low-dose Dexamethasone Suppression Test This blood test is run in the hospital and requires 3 blood samples. The first sample is taken before the dexamethasone injection, the 2nd sample at 4 hours after the injection and the 3rd sample at 8 hours after the injection. High cortisol readings at every reading are indicative of adrenal-related Cushing’s and a moderate decrease in cortisol levels may indicate pituitary-related Cushing’s. THIS IS USUALLY THE FIRST SCREENING TEST WE USE AT CRONULLA VETERINARY CLINIC
High-dose Dexamethasone Suppression Test 

This blood test is run in the hospital and requires 3 blood samples. This test helps to distinguish between pituitary-related and adrenal-related Cushing’s disease and is run when there is no reduction in cortisol levels after a Low-dose dexamethasone suppression test. A reduction in cortisol levels after a higher dose of dexamethasone may indicate pituitary-related Cushing’s and no change in levels may indicate an adrenal-related Cushing’s disease. NOT ROUTINELY USED.

 

Diagnostic imaging tests

Radiographs or ultrasound May be required to determine whether an adrenal tumour is present. 
MRIs or CTs

May be required to determine if a pituitary or adrenal tumour is present.