HAC diagnostic testing

Question 1

Why is diagnosing HAC so difficult?

Answer 1

Because there are 3 different conditions you need to distinguish between:
Psychological stress/ chronic illness
PDH
ADH

Question 2

Which parameters are increased and which are decreased?

Answer 2

Increased:
ALP
ALT
Cholesterol
Fasting glucose
Bile acid

Decreased= Urea (BUN)

Question 3

What impact does the stress response have on the CBC?

Answer 3

-Neutrophilia and lymphopenia (low lymphocytes)

Question 4

Using the SpIn and SnOut rules which means having confidence in the negative result and which is having confidence in a positive result?

Answer 4

• SpIN= extreme confidence in a positive result (specificity)
• SnOut= extreme confidence in a negative result (sensitivity)

Question 5

What does a test with high sensitivity refer to?

Answer 5

The test’s ability to correctly detect patients who DO HAVE the disease
-You work out the sensitivity by dividing the true positive over the sum of the true positives plus the false negatives

Question 6

List the screening test options for HAC

Answer 6

• Urinary cortisol: creatinine ratio
• ACTH stimulation test
• Low dose dexamethasone suppression test

Question 7

Discuss the urinary cortisol: creatinine ratio test

Answer 7

• Screening test used for HAC
• High sensitive but not very specific
• Low ratio makes HAC very unlikely -SnOut

Question 8

Discuss the ACTH stimulation test

Answer 8

-Protocol:
Starve overnight
Take blood sample
Inject with exogenous ACTH
Wait 60 mins then take second blood sample

Normal result= 1st ~200 and 2nd ~600
Positive result= 2ns higher than 600

Ok sensitivity but HIGH specificity= SpIn

Test shows up iatrogenic chusings too= have no reaction due to adrenal cortex not functioning, is caused by long steroid course

Question 9

Discuss the LDDS test

Answer 9

• Requires prolonged hospital stay
• Measure baseline plasma cortisol
• Inject dexamethasome (exogenous glucocorticoid)
• Measure again at 3/ 8 hours post injection
• Normal response:exogenous glucocorticoid should have a neg feedback effect on ACTH release and hence lower plasma cortisol.
• HAC animals have a reduced/ absent response (plasma cortisol stays high)
• Expect PDH to have a 50% suppression then increase again, but not all PDH dogs respond this way. So less useful at distinguishing between ADH and PDH
• Very sensitive, less specific
• SnOut

Question 10

Which form of cushings (ADH or PDH) respond better to treatment?

Answer 10

PDH.

-ADH is more resistant to medical management

Question 11

Which tests can you use to distinguish between ADH and PDH?

Answer 11

HDDS
Endogenous ACTH
Adrenal imaging
Pituitary imaging

Question 12

Why is HDDS no longer a recommended test?

Answer 12

-25-30% of PDH cases still fail to suppress as expected

Question 13

Why do ADH cases not suppress during an LDDS or HDDS test?

Answer 13

-Because adrenocortical tumours are autonomous- so ACTH levels have no affect on them.

Question 14

How does endogenous ACTH help distinguish between PDH and ADH?

Answer 14

• PDH can fall within normal range whereas ADH cases do not.

- Dogs with functional adrenal tumours produce a lot of cortisol- therefore ACTH is already supressed.

Question 15

What do you expect to see when performing adrenal imaging on both PDH and ADH cases?

Answer 15

PDH= symmetrical enlargement
ADH= one enlarged and one atrophied, may see invasion of a malignant tumour and may see calcification