Canine Adrenal Testing - Which Test Should I Run?

By Jennifer S. Fryer, DVM

Urine Cortisol:Creatinine Ratio:

· Screening test for Hyperadrenocorticism (Cushing’s or HAC)

· Low Cost, Easy to collect (voided morning urine at home)

· Normal value rules out Hyperadrenocorticism

· Elevated values can indicate stress or Hyperadrenocorticism & adrenal function testing is necessary.

Baseline Cortisol:

· Screening test for Hypoadrenocorticism (Addison’s)

· Values >2 mcg/dl rule out Hypoadrenocorticism (Addison’s)

· Cannot be used to diagnose Hyperadrenocorticism (Cushing’s)

ACTH Stimulation Test:

· Test of choice to diagnose Hypoadrenocorticism (Addison’s)

· Screening test for Hyperadrenocorticism (Cushing’s)

· Used to monitor Trilostane or Lysodren Therapy

· Can be used to differentiate spontaneous vs. iatrogenic HAC

· 60-85% of dogs with HAC will have a positive result on this test.

· 85-90% of dogs without HAC will have a negative result on this test.

· Advantages:

o Can be completed in 1 hour

o No special handling of samples

o Submit for extended Adrenal Panel to document Atypical HAC

· Disadvantages:

o High cost of Cosyntropin

o Low Sensitivity (false negatives are possible)

Low-Dose Dexamethasone Suppression Test:

· Screening test for Hyperadrenocorticism (Cushing’s)

· Helps differentiate pituitary vs. adrenal origin

· 85-95% of HAC dogs have a positive result.

· 70-75% of dogs without HAC have a negative result.

· 40% of dogs with PDH and all adrenal tumor dogs have dexamethasone resistance and will require another differentiating test.

· Advantages:

o Low cost

o Higher sensitivity than ACTH Stim

o No special handling of samples

· Disadvantages:

o All day test requiring three blood samples at 0, 4, 8 hours

o The dog should be kept as minimally stressed as possible during this 8 hour period

High-Dose Dexamethasone Suppression Test:

· Theoretically helps differentiate Hyperadrenocorticism of pituitary vs. adrenal origin.

· Similar results to Low-Dose Dexamethasone Suppression Test at 8 hours.

· Rarely performed.

Endogenous ACTH Measurement:

· Helps differentiate pituitary vs. adrenal HAC

· Single plasma sample required

· Sample handling is difficult & critical to accurate measurement.

· With proper sample handling, this test is very reliable at differentiating pituitary vs. adrenal HAC.

Abdominal Ultrasound:

· Helps differentiate pituitary vs. adrenal HAC.

· May identify adrenal tumor, local invasion or metastasis.

· High cost

· Adrenals can be normally sized in PDH

· Adrenals can be difficult to visualize in some animals

· Ultrasound does not always accurately identify extent of metastasis or local invasion of an adrenal tumor

Computed Tomography (CT Scan):

· Screening test for Pituitary Tumor or Primary Adrenal Tumor and abdominal metastasis &/or local invasion

· Brain CT is not indicated unless a macroadenoma is suspected.

· Very high cost.

· Requires anesthesia.

· Cannot detect 50% of pituitary masses.

· Cannot differentiate between functional and non-functional tumors. Adrenal function tests are still required.

Brain Magnetic Resonance Imagine (MRI):

· Screening test for Pituitary Tumor

· Brain MRI is not necessary unless a macroadenoma is suspected.

· More reliable than CT at detecting small pituitary masses.

· Very high cost.

· Requires anesthesia.

· Not indicated unless a macroadenoma is suspected.

· Cannot differentiate between functional and non-functional tumors. Adrenal function tests are still required.

References

Lennon EM, Boyle TE, Hutchins RG, et al. Use of basal serum or plasma cortisol concentrations to rule out a diagnosis of hypoadrenocorticism in dogs: 123 cases (2000-2005). J Am Vet Med Assoc 2007;231(3):413-6.

Nelson RW, Turnwald GH, Willard MD. Endocrine, Metabolic, and Lipid Disorders. In: Willard MD and Tvedten H, eds. Small Animal Clinical Diagnosis by Laboratory Methods. 4^th edition. St. Louis: Elsevier Saunders, 2004:165-207.

Reusch, CE. Hyperadrenocorticism. In: Ettinger SJ and Feldman EC, eds. Textbook of Veterinary Internal Medicine. 6^th edition. St. Louis: Elsevier Saunders, 2005:1592-1611.

Severe DKA and Severe Financial Constraints - What are the Options?

Ms. Smith brings in her 14 year old cat Mama Cat. The cat is a diabetic who receives twice daily insulin. Ms. Smith tells you that she hasn’t come back for a glucose curve for the last year because she couldn’t afford it. She thought Mama Cat was doing OK on her dose of insulin. The cat started vomiting a few days ago. Ms. Smith came home from work today to find that Mama Cat can’t get up. She wants to do everything possible for Mama Cat, but wants to do it inexpensively. And she promises to heed your advice on follow-up visits in the future.Mama Cat is hypothermic and obtunded. A blood glucose is >600 and the cat has 1+ ketones in her urine. Ms. Smith has declined referral to the local 24 hour clinic. You are uncomfortable managing such a sick cat. But Ms. Smith really wants you to treat her. You look in the fridge. Your bottle of Regular Insulin expired a month ago - a testament to the fact that it has been a long time since you have treated a DKA. What should you do now?

First of all, don’t worry. If you can get an IV catheter & fluids in Mama Cat, you have made huge progress towards saving her. The first thing Mama Cat needs is fluid resuscitation. You can worry about the insulin later, once she is better hydrated. That gives you plenty of time to send your assistant to the drug store to get some more Humulin R. Once you have that insulin, you can use the IM technique, which requires less monitoring for you & your staff and less expense for the owner. It works just as well as a CRI of insulin. Control her nausea with metoclopramide to get her eating (or put an NE tube in). You will find that her glucose, potassium, and phosphorus will regulate faster and with less need for monitoring.

We frequently receive calls like this at Veterinary Answers. We will talk you through the steps you need to take and send you a written report to use as your guide. We want Mama Cat to pull through just as much as you do. And we will be there for you every step of the way.

Focus on Referral Issues

This article in the recent issue of Trends Magazine, highlights many of the issues that prompted me to found Veterinary Answers. AAHA held forums to promote better relationships between general practitioners and specialists. The forums were held in Denver, CO; Orange County & Fremont, CA; Houston, TX; Chicago, IL; Boston, MA; and Washington, DC and were attended by 121 specialists & 74 general practitioners. Unfortunately, specialists were overrepresented. But I think the results are pertinent.

Please add your perspective on these issues, too.

The Referring Veterinarian’s Perspective

• They would like “mutual respect and a non-judgmental attitude” in communications with specialists.
• They prefer that their calls be returned during business hours.
• They would like to have a specialist give due to consideration to consultations and advice on cases that cannot be referred.

The Specialist’s Perspective

• Because of busy schedules, they return most calls after hours.
• Most specialists return consult calls last.
• Specialists are hesitant to discuss advice when a case is not going to be referred.
• They are also hesitant to give advice on cases they have not seen for a long time.

I have been on both sides here. It is so frustrating to have a difficult case that cannot be referred, yet you and owner desperately want to help the animal. I have also been the busy specialist who didn’t see her less urgent messages until she could finally sit down at her desk at 8:30 in the evening, long after most veterinarians (hopefully) have gone home. I can’t tell you how many consults I gave on the fly to a vet who needed help. I gave the best advice I could while juggling several issues at once (an occasionally with an ultrasound probe in my hand). It wasn’t fair to anyone. My advice wasn’t as well reasoned as it should have been, I probably sounded stressed, and the veterinarian at the other end of the phone did not receive any documentation of our conversation. While doing referral work, most of my time was spent talking with owners and RDVMs about hospitalized cases, doing ultrasound, and SOAPing patients. Everything else developed a low priority so that my patients could receive the best care. Something had to give, and unfortunately, it was often the referring veterinarians who paid the price.

Veterinary Answers gives calling veterinarians their undivided attention. Every call is followed with a written report that is faxed or emailed to the veterinarian to document the conversation. We work together with veterinarians to advance the level of care they give all of their patients. We understand the limitations veterinarians face, from owner financial constraints to limited resources. Together, we will work with you to help your patients despite these obstacles.

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• • • Geriatric screening
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• • • Emergency Treatment & Diagnosis of the Dyspneic Patient
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Veterinary Answers Partners with Diagnostic Vet Labs

In the Los Angeles metropolitan area, Veterinary Answers has partnered with Diagnostic Vet Labs to offer internal medicine consultations through the lab on their lab work.

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Contact DVL at (800) 247-8621 to set up a DVL account.

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Tell us what else you would like to see.