adjust to normal. If steroids are abruptly withdrawn, the dormant adrenal glands may not able to reactivate, and the body will need to have its adrenal glucocorticoid hormones replaced by medication. Diagnosis Hypoadrenocorticism is often tentatively diagnosed on the basis of history, physical findings, clinical pathology, and, for primary adrenal insufficiency, characteristic electrolyte abnormalities. Clinical pathology - Abnormalities may be identified on hematology, biochemistry and urinalysis. Elevated concentrations of potassium (hyperkalemia), and low sodium and chloride values (hyponatremia and hypochloremia) are the classic electrolyte alterations. The sodium/potassium ratio often is <27 (normal is between 27:1 and 40:1) and maybe <20 in animals with primary adrenal insufficiency. However, not all dogs have an abnormal electrolyte ratio during an Addisonian episode. ECG - The severity of the ECG abnormalities correlates with the severity of the hyperkalemia. Therefore, the ECG can be used to identify and estimate the severity of hyperkalemia and to monitor changes in serum potassium during therapy. Diagnostic imaging - Abdominal ultrasound may reveal small adrenal glands, suggesting adrenocortical atrophy. However, finding normal-sized adrenal glands does not rule out hypoadrenocorticism. Rarely, megaesophagus is evident on radiographs. ACTH stimulation test - Confirmation requires evaluation of an ACTH stimulation test. Baseline plasma cortisol and urine cortisol/Cr ratios are unreliable for confirming the diagnosis. One major diagnostic criterion is abnormally decreased post-ACTH plasma cortisol. Normal plasma cortisol after ACTH stimulation rules out adrenal insufficiency. The only accurate test for hypoadrenocorticism is an ACTH stimulation test; however, any administration of a steroid other than dexamethasone will invalidate this test. Carry out test by: Measuring serum cortisol before and after administration of ACTH gel or synthetic ACTH Normal dogs generally have post stimulation cortisol levels > 10 ug/dl. Post stimulation levels < 2 ug/dl is considered diagnostic and most Addison's patients are < 1 ug/dl. The ACTH stimulation test does not distinguish between primary and secondary hypoadrenocorticism, or adrenocortical destruction caused by mitotane overdose. Differentiation between primary and secondary hypoadrenocorticism can be made by periodically measuring serum electrolytes, baseline endogenous ACTH, or possibly serum or plasma aldosterone during the ACTH stimulation test. While most corticosteroid drugs will invalidate the results of an ACTH test, dexamethasone may be used in the event of an Addison's emergency without fear of compromising the results of the test. In general, hypoadrenocorticism is underdiagnosed in dogs, and one must have a clinical suspicion of it as an underlying disorder for