What is the best test to diagnose hypercortisolism?

     Unfortunately, there is no easy answer as there is no gold standard test that will diagnose hypercortisolism. The most straight forward diagnoses are in dogs with typical clinical signs that have routine clinicopathological changes suggestive of hypercortisolism and an ACTH stimulation test, low dose dexamethasone suppression and diagnostic imaging confirm the diagnosis and localise the lesion.

I have a case with high ALP but no signs or other clinicopathological changes, does it have hypercortisolism?

     This is a slowly progressive disease, and dogs should have consistent clinical signs prior to the undertaking of investigations, otherwise what are you treating? Increased ALP activity alone is not toxic to dogs. Wait and see what happens and if signs develop then investigate as appropriate.

Can synthetic ACTH be given intramuscularly?

     Yes, synthetic ACTH can be given intramuscularly, but it stings! Synthetic ACTH should
be given intravenously in dehydrated or collapsed animals e.g. Addisonian crisis as it may not be absorbed well otherwise. Dogs with hypercortisolism are typically well hydrated and not collapsed.

Should a dog undergoing LDDS be fasted?

     Fasting may be a stressor for some dogs, during a LDDS test stress should be kept to a minimum. Feeding a small volume of low-fat food may prevent a dog becoming overly stressed and avoiding this influence on the results. If fasting is necessary, feed after the 3 hour sample as there are 5 hours until the next sample is taken.

Can ACTH stim and BAST be performed on the same day?

     Why would this be necessary? Two separate diseases are being investigated and hypercortisolism will cause some increase in bile acids meaning results may not be clear. If it is necessary to do so 3 blood samples will be required, start with basal cortisol, give ACTH, take second sample 1 hour later and then feed the dog. Use the second sample for post ACTH cortisol and pre-prandial bile acids. Take post prandial bile acid sample 2 hours later.

Can other diagnostic tests such as imaging be performed on the same day?

     Other tests can be performed on the same day as ACTH stimulation test and LDDS but only after these tests have been completed. Do not perform ACTH stimulation test and LDDS on the same day. They can be performed on consecutive days.

Can I sedate a dog to perform ACTH stimulation test or LDDS?

     No, this is not recommended during the investigation of hypercortisolism as the stress may influence the results. If a dog has hypoadrenocorticism stress will not influence its ability to produce cortisol and ACTH stimulation test can be performed with sedation (the dogs are usually so sick it is not required).

My patient is receiving steroids, and I want to test for hypercortisolism, do I need to
stop the medication? 

     Even small doses of glucocorticoids can cause signs of iatrogenic hypercortisolism. An ACTH stimulation test can be performed if the dog has not received steroids for 24 hours (the assay can measure the exogenous steroid in some cases) to see if there is either a poor or blunted response. If there is a poor/blunted response following ACTH administration this suggests iatrogenic hypercortisolism, an excessive response could suggest hypercortisolism.

I have done all the routine tests for hypercortisolism but cannot confirm its presence, what will I do?

     This is very uncommon. Does the dog look like it has hypercortisolism and have appropriate signs? Have you ruled out other differential diagnoses? If this is the case, consider urine cortisol to creatinine ratio and potentially followed by advanced imaging (CT scan of the brain) and pair it with eACTH. If this is not possible but you are convinced by the appearance and signs that the dog has the disease a well planned and monitored treatment trial could be considered. Trilostane is not a benign medication and definitive goals such as resolution of Pu/Pd and improvement of appearance should be defined.