398 DISEASES/DISORDERS
“Gold standard” for diagnosis of iatrogenic HAC: baseline cortisol levels will be
below normal and will not increase with stimulation
Best test for diagnosis of spontaneous Addison’s disease (hypoadrenocorticism).
Glucocorticoids, progestagens, and ketoconazole may suppress cortisol secre-tion; phenobarbital does not appear to influence test results
Testing methodology:
Fasted patient: hemolysis and lipemia may affect values
Promptly spin and separate the serum or plasma before refrigeration
Baseline cortisol sample
Inject 5μg/kg IV or IM of cosyntropin or tetracosactrin (use of compounded
ACTH is discouraged)
Second blood sample at 1 hour post injection
Test interpretation:Poststimulation cortisol> 22 μg/dL consistent with HAC (check laboratory
standard values)
Poststimulation cortisol< 15 μg/dL not consistent with HAC: 20–30% of
patients with HAC stimulate below the cut-off
Nonadrenal illness may yield a false-positive result
Both pre- and postcortisol values are blunted – consider iatrogenic HAC. LDDST:
95% sensitive, 44–73% specific
Screening test to identify HAC
Testing methodology:
Fasted patient: hemolysis and lipemia may affect values
Promptly spin and separate the serum or plasma before refrigeration
Baseline cortisol sample
Inject 0.01 mg/kg of dexamethasone intravenously (dilute in 0.9% sodium
chloride solution for accuracy in dosing)
Second sample at 4 hours post administration
Third sample at 8 hours post administration
Test interpretation:
Normal: suppression<50% of baseline and<1.5μg/dL at 8 hours
Lack of suppression to<50% baseline and<1.5μg/dL at 8 hours confirms
HAC; if no suppression is noted, cACTH measurement or abdominal ultra-
sound is recommended
Suppression to<50% baseline and<1.5μg/dL at 4 hours but lack of sup-
pression at 8 hours is most consistent with PDH
Lack of suppression does not confirm an adrenal tumor; 25% of dogs with
PDH fail to suppress<1.5μg/dL; nonadrenal illness can affect the test.
Urine cortisol-creatinine ratio:
UCCR provides a reflection of cortisol production; day-to-day variation
Screening test to be used in conjunction with LDDST
Cannot be used to monitor treatment
Negative result means HAC is unlikely; positive result indicates need for confir-
matory testing