Page 895 - Small Animal Internal Medicine, 6th Edition

CHAPTER 50 Disorders of the Adrenal Gland 867

on diagnosis of spontaneous canine hyperadrenocortisim mornings by the client in the nonstressful home environ-
are given in Box 50.4 (Behrend et al., 2013). Ideally, testing ment. The stress associated with driving the dog to the vet-
VetBooks.ir for hyperadrenocorticism should be avoided if serious illness erinary hospital and having the dog undergo a physical
examination before urine is collected can influence test
exists. Many illnesses affect results of screening tests for
hyperadrenocorticism. Testing for hyperadrenocorticism is
between different urinary cortisol assays so it is important
not mandatory at the time suspicion arises. Postponing results (Fig. 50.11). There is considerable variation in results
testing until concurrent illness is resolved or controlled is that an assay specific reference range is established by the
recommended, but the current illness must be considered laboratory used to determine UCCRs. A normal UCCR in
when interpreting test results (Behrend et al., 2013). one or both urine samples serves as evidence against hyper-
adrenocorticism. Normal UCCR test results can occur in
Urine Corticoid/Creatinine Ratio dogs with hyperadrenocorticism but are very uncommon.
The UCCR is an excellent initial screening test for hyperad- Increased UCCR in both urine samples is supportive of but
renocorticism in dogs. The UCCR should be determined not definitively diagnostic for hyperadrenocorticism. The
from free-catch urine samples collected on two consecutive reported sensitivity and specificity of the UCCR measured
on a single urine sample ranges from 75% to 100% and 20%
to 25%, respectively in dogs. The UCCR is often increased
BOX 50.4 in dogs with nonadrenal illness and in dogs with clinical
signs consistent with hyperadrenocorticism but with a
Indicators for Performing Diagnostic Tests for normal pituitary-adrenocortical axis (Fig. 50.12). Additional
Hyperadrenocorticism in Dogs* tests are indicated when the UCCR is increased or when the

• Compatible history and physical examination findings; UCCR is normal but the clinical picture strongly suggests
the greater the number of findings, the stronger the hyperadrenocorticism.
suspicion
• A pituitary macrotumor Low-Dose Dexamethasone
• A diabetic dog with persistently poor response to high Suppression Test
dosages of insulin not attributed to another cause The LDDS test is considered the screening test of choice for
including owner issues hyperadrenocorticism unless iatrogenic hyperadrenocorti-
• An adrenal mass cism is suspected (Behrend et al., 2013). In the normal dog
• Biochemical, complete blood count, urinalysis, and relatively small doses of dexamethasone given intravenously
urine protein:creatinine ratio and blood pressure can inhibit pituitary secretion of ACTH, causing a prolonged
measurements, by themselves, are not indicators to test
decline in the serum cortisol concentration (Fig. 50.13).
*From: Behrend EN et al.: Diagnosis of spontaneous canine Dexamethasone is used because it does not interfere with the
hyperadrenocorticism: 2012 ACVIM consensus statement (Small assays used to measure cortisol. The abnormal pituitary in
Animal), J Vet Intern Med 27:1292, 2013. dogs with PDH is somewhat resistant to the negative

30.0 30.0 Hospitalization

Urinary C:C ratio (×10 -6 ) 20.0 Urinary C:C ratio (×10 -6 ) 20.0

10.0
10.0

0.0 0.0
1 2 3 1 2 3 4
A Days B Days
FIG 50.11
Urinary corticoid/creatinine (C:C) ratio measured in 12 pet dogs before and after a visit
to a referral clinic for orthopedic examination (A) and in 9 healthy pet dogs before,
during, and after a 1.5-day hospitalization at a referral clinic (B). The arrows indicate
time of visit to the referral clinic. Note the increase in the urinary C : C ratio in a few
dogs, affiliated with a visit to a veterinary practice. (From van Vonderen IK et al.:
Influence of veterinary care on the urinary corticoid:creatinine ratio in dogs, J Vet Intern
Med 12:431, 1998.)