Hi again, Amanda. I’m going to jump back in and give you a quote from an article published by a researcher at University of Tennessee at Knoxville that perhaps best answers your question about testing for “Atypical Cushing’s.” As you’ll see, Dr. Oliver is describing dogs who exhibit Cushing’s-like symptoms and also elevated cortisol on urine creatinine: cortisol tests, but who test negative for elevated cortisol on the LDDS and ACTH stimulation test for cortisol alone.

HYPERESTRINISM IN DOGS
Jack W. Oliver, D.V.M., Ph.D.
Director, Clinical Endocrinology Service
The University of Tennessee

The Clinical Endocrinology Service at the University of Tennessee utilizes steroid hormone profiling in the diagnosis of adrenal disease. Many of the cases received have had preliminary diagnostic workups with either ACTH stimulation or low dose dexamethasone suppression testing that has been negative, but signs of Cushing's disease persist. Many of these atypical Cushing's-like cases will have abnormal levels of adrenal intermediate steroids and sex hormones. Included in the atypical cases are a considerable number of dogs that have hyperestrinism (elevated estradiol levels), with and without increased levels of other steroids. The dogs with hyperestrinism typically present with some or all of the following clinical signs: “Cushingoid” appearance, presence of chronically elevated levels (usually extremely elevated) of serum alkaline phosphatase, hepatomegaly, steroid hepatopathy on biopsy, PU/PD, dilute urine, panting, haircoat problems and skin biopsies that indicate presence of an endocrinopathy. The talk will focus on case presentations that associate clinical signs presented by dogs with primary hyperestrinism (elevated serum estradiol levels), including the association of high estradiol with increased alkaline phosphatase, and the fact that sex steroids can cause elevated cortisol/creatinine ratios. Treatment concerns will be addressed, such as mitotane and trilostane resistance. Other potential treatments for hyperestrinism will be discussed.
Unfortunately, Dr. Oliver passed away a few years ago. But other researchers at Univ. of Tennessee are still carrying on related research.

https://vetmed.tennessee.edu/vmc/dls...s/default.aspx

Also, there’s a lot of other helpful information, on this thread:

https://www.k9cushings.com/forum/sho...Hyperestrinism

As far as other additional testing for Yohnny, you’ve mentioned that an abdominal ultrasound has already been done? If so, we’d hope that the adrenal glands were seen on that scan. Sometimes during the early stages of Cushing’s, the glands may still look normal, though. As far as other testing, a urinalysis can be very helpful — Cushing’s dogs typically exhibit very dilute urine with low specific gravity.

Marianne