Home > Endocrinology, Laboratory Tests, Recent Literature, Ultrasound > Canine Adrenal Testing – Which Test Should I Run?

Canine Adrenal Testing – Which Test Should I Run?

By Dr. Jennifer S. Fryer

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. 4th edition. St. Louis: Elsevier Saunders, 2004:165-207.

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

 

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  1. August 6, 2013 at 7:08 am

    I read somewhere that there was another method of diagnosing canine hyperadrenocorticism from just examining the fur. How do you think this can be done?

    • August 6, 2013 at 3:05 pm

      You are correct. This article – Evaluation of Hair Cortisol in the Diagnosis of Hypercortisolism in Dogs – was just published in JVIM. The investigators measured cortisol in the hair of healthy dogs, dogs sick with diseases other than hyperadrenocorticism, and dogs with hyperadrenocorticism. With a 91% sensitivity and 61% specificity to diagnose hyperadrenocorticism, it could be another diagnostic test we could use in the future to rule in or out HAC. However, the sample sizes were small, so further investigation is warranted. I hope there will be more data soon!

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