Veterinary Medicine - February 2009 - (Page 70) ClinQuiz A NS W ERS tration is 10 µg/dl at baseline and 4 µg/dl eight hours after dexamethasone administration, thus the dog exhibits at least 50% cortisol suppression at some point during the test, which is diagnostic for PDH. E—Incorrect. The cortisol concentration is 10 µg/dl at baseline and 4 µg/dl eight hours after dexamethasone administration, thus the dog exhibits at least 50% cortisol suppression at some point during the test, which is diagnostic for PDH. eight hours after dexamethasone administration, thus the dog exhibits at least 50% cortisol suppression at some point during the test, which is diagnostic for PDH. E—Incorrect. The cortisol concentration is 10 µg/dl at baseline, 4 µg/dl four hours after dexamethasone administration, and 10 µg/dl eight hours after dexamethasone administration, thus the dog exhibits at least 50% cortisol suppression at some point during the test, which is diagnostic for PDH. ever, up to 10% of dogs with PDH will have normal LDDS test results. Thus, in dogs with clinical signs of hyperadrenocorticism and normal LDDS test results, you may want to perform an ACTH stimulation test next or wait four to six weeks and repeat the LDDS test.) D—Incorrect. In dogs with a normal cortisol concentration eight hours after dexamethasone administration and, thus, a normal LDDS test result, it is inappropriate to attempt to distinguish between PDH and ADH. E—Correct. Although the baseline cortisol concentration is high and greater than 50% cortisol concentration suppression occurred during the test, the eight-hour postdexamethasone administration cortisol concentration is 2 µg/dl eight hours after dexamethasone administration, which is diagnostic for hyperadrenocorticism. B—Incorrect. As discussed earlier, dogs with adrenal tumors will never exhibit cortisol concentration suppression with an LDDS test. C—Correct. The cortisol concentration is 10 µg/dl at baseline, 4 µg/dl four hours after dexamethasone administration, and 10 µg/dl eight hours after dexamethasone administration, thus the dog exhibits at least 50% cortisol suppression at some point during the test, which is diagnostic for PDH. This inverted, or escape, pattern of suppression is the most common LDDS test result seen in the laboratory. The increase in cortisol concentrations between four and eight hours after dexamethasone administration reflects the accelerated dexamethasone metabolism that often occurs in dogs with hyperadrenocorticism. D—Incorrect. The cortisol concentration is 10 µg/dl at baseline, 4 µg/dl four hours after dexamethasone administration, and 10 µg/dl line cortisol concentration is high, the eight-hour postdexamethasone administration cortisol concentration is < 2 µg/dl, which is within the reference range for this test. (However, keep in mind that up to 10% of dogs with PDH will have normal LDDS test results. Thus, in dogs with clinical signs of hyperadrenocorticism and normal LDDS test results, you may want to perform an ACTH stimulation test next or wait four to six weeks and repeat the LDDS test.) B—Incorrect. Although the baseline cortisol concentration is high, the eight-hour postdexamethasone administration cortisol concentration is < 2 µg/dl, which is within the reference range. C—Incorrect. Although the baseline cortisol concentration is high and greater than 50% cortisol concentration suppression occurred during the test, the eight-hour postdexamethasone administration cortisol concentration is < 2 µg/dl, which is within the reference range. (How- This quiz was provided by David S. Bruyette, DVM, DACVIM, VCA West Los Angeles Animal Hospital, 1818 S. Sepulveda Blvd, West Los Angeles, CA 90025. 70 February 2009 VETERINARY MEDICINE
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