HAC diagnostic testing

Question 1

Why is diagnosis of HAC difficult?

Answer 1

PDH, ADH and psychological stress, chronic illness all cause an increase in cortisol

Question 2

What biological abnormalities would make you suspicious of HAC?

Answer 2

Elevated:
- ALP
- ALT
- Cholesterol
- Bile acids
Reduced:
- urea

Question 3

What complete blood count changes would make you suspicious of HAC?

Answer 3

Neutrophilia (high neutrophils)
Lymphopenia (low lymphocytes)

Question 4

What USG would make you suspicious of HAC?

Answer 4

Low USG (<1.015 or hyposthenuric/<1.008)
Evidence of UTI

Question 5

What radiographic findings would make you suspicious of HAC?

Answer 5

Question 6

What ultrasonographic findings would make you suspicious of HAC?

Answer 6

Hyperplastic adrenals with normal echogenecity
Both enlarged = PDH
One enlarged = ADH

Question 7

What screening tests are used for diagnosing HAC?

Answer 7

Urinary cortisol:creatinine ration
ACTH stimulation test
Low dose dexamethasone suppression (LDDS) test

Question 8

Describe the use of urinary cortisol:creatinine ration in HAC diagnosis

Answer 8

Urine sample collected at home in the morning
Low ratio makes HAC extremely unlikely (high sensitivity)
High ration could be HAC, also elevated in other diseases (low specificity)

Question 9

Describe the process of an ACTH stimulation test in diagnosing HAC

Answer 9

Starved overnight
Injection of exogenous ACTH results in increased cortisol release from adrenal gland
=> exaggerated raise in cortisol in dogs with HAC

Question 10

what is a positive results in an ACTH stim test for diagnosing HAC?

Answer 10

Question 11

Describe the reliability of ACTH stimulation in diagnosing HAC

Answer 11

OK sensitivity - don’t exclude HAC if negative
Best specificity of HAC tests - few false positives

Question 12

Describe the process of an LDDS test in diagnosing HAC

Answer 12

Starve overnight
Injecting dexamethasone (exogenous glucocorticoid - acts in same way as cortisol) => reduced ACTH due to -ve feedback
Cortisol measured at 3 and 8 hrs after
Suppressed cortisol from adrenal gland expected if healthy
No/less suppression in HAC

Question 13

Describe the reliability of the LDDS test for diagnosing HAC

Answer 13

More sensitive - fewer false negatives
lower specificity - more false positives

Question 14

Describe the different possible results of the LDDS test when diagnosing HAC

Answer 14

Question 15

What is the treatment option for dogs with ADH?

Answer 15

Normally resistant to medical management
Adrenalectomy is option

Question 16

Why methods can be used to differentiate between ADH and PDH?

Answer 16

High dose dexamethasone suppression test (HDDS)
Endogenous ACTH
Adrenal imaging
Pituitary imaging

Question 17

Describe how a HDDS test can be used to differentiate between ADH and PDH

Answer 17

PDH - HD dexamethasone lowers ACTH => lowers cortisol (not all cases so not a recommended test)
ADH - HD dexamethasone has no effect on ACTH as it is already low => no change in cortisol

Question 18

How can endogenous ACTH be used to differentiate between ADH and PDH?

Answer 18

ADH - low ACTH
PDH - high ACTH (can fall in normal range)
Used to diagnose ADH

Question 19

How can adrenal imaging be used to differentiate between ADH and PDH?

Answer 19

PDH - symmetrically enlarged and normal conformation
ADH -one enlarged gland, one atrophied gland