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Copying from www.k9cushings.com/forum. Much of the following is technical but mind come in handy depending on test results. The UCCR information is fairly straightforward.
To download the PDF, follow this link.
http://wvc.omnibooksonline.com/data/papers/2009_V101.pdf
Low Dose Dexamethasone Test (LDDS)
The protocol utilized for this test is obtaining plasma samples for cortisol before and 4 and 8 hours after I.V. administration of 0.01 mg/kg dexamethasone. The 8-hour plasma cortisol is used as a screening test for hyperadrenocorticism, with concentrations >1.4 μg/dl being consistent with (not confirming) the diagnosis of Cushing's syndrome. This test is relatively sensitive and specific, but not perfect. Approximately 90% of dogs with Cushing's syndrome have an 8 hour postdexamethasone
plasma cortisol concentration >1.4 μg/dl and another 6 to 8% have values of 0.9 - 1.3 μg/dl. The results of a low dose test can also aid in discriminating PDH from ACT, using three criteria: 1) an 8 hour plasma cortisol >1.4 μg/dl but <50% of the basal value; 2) a 4 hour plasma cortisol concentration <1.0 μg/dl; and 3) a 4 hour plasma cortisol concentration <50% of the basal value. If a dog has Cushing's and it meets any of these three criteria, it most likely has PDH. Approximately 65% of dogs with naturally occurring PDH demonstrate suppression, as defined by these three criteria. A dog with Cushing's that fails to meet any of these three criteria could have either PDH or ACT. However, if it has two relatively equal sized adrenals on abdominal ultrasonography, it most likely has PDH.
ACTH Stimulation (NO LONGER RECOMMENDED)
note: for diagnosing, that is....still the test to use to monitor a dog on treatment, tho)
The ACTH stimulation test has been popular for decades in veterinary medicine. It is simple to complete and takes little time. The other significant feature regarding results of an ACTH stimulation test is that this is the only study which reliably demonstrates the effect of o,p' DDD on the adrenal cortex. Thus, some veterinarians want results of an ACTH stimulation test, prior to initiating o,p' DDD therapy, because the results are used as “baseline” information to objectively monitor effects of o,p' DDD. Regardless of the protocol chosen, it must be appreciated that 20 - 30% of dogs with Cushing's syndrome have test results within the reference range (in our laboratory: post ACTH plasma cortisol concentrations of 6 to 17 μg/dl). An additional 20 - 30% of dogs with Cushing's have test results described as “borderline” (plasma cortisol concentrations >17 but <22 μg/dl). Therefore, the test is not considered sensitive but is relatively specific, i.e., those dogs with plasma cortisol concentrations >22 μg/dl frequently have Cushing's. However, specificity of an exaggerated response to ACTH is also not perfect. Therefore, test results should never be interpreted without knowing results of history, physical examination, and routine data base testing. There are no features of ACTH stimulation test result that allow discrimination between PDH and ACT. As ACTH has become more and more expensive, this test is losing popularity. .... In our opinion, the lack of sensitivity of the ACTH stimulation test makes it a test that the profession should abandon. The situations in which ACTH stimulation testing would be indicated include monitoring therapy for naturally occurring hyperadrenocorticism, to aid in the diagnosis of iatrogenic Cushing's syndrome, and as the “gold standard” for the diagnosis of naturally occurring hypoadrenocorticism (addison's disease).
Urine Cortisol: Creatinine Ratio (UC:CR)
The urine UC:CR ratio is easily performed (simply have the owner collect and deliver urine to the hospital and submit it to the laboratory) and, therefore, it is usually less expensive than other screening tests. Most dogs (~97%) with naturally occurring Cushing's syndrome have an abnormal result (the test is sensitive) but a significant percentage of dogs with polyuria / polydipsia due to other conditions and those with non-endocrine illness also have abnormal results (the test is not specific). It has been suggested that the UC:CR be routinely performed only on urine collected by an owner at home, rather than having it collected inhospital. Since this protocol eliminates travel or hospital stress from altering test results, it seems reasonable to follow this concept. We do not utilize this test with the same degree of confidence with which we use the low dose dexamethasone screening test. However, a normal result is quite uncommon in a dog with Cushing's syndrome while an abnormal result could be used to prompt further testing. Therefore, this test can be used as a prompt to recommend abdominal ultrasonography and a low dose dexamethasone test to an owner.
_________
Separately, Dr. Bruyette, an IM who specializes in endocrinology, discussed the need for a three-day pooled sample.
Urine cortisols can be a problem. Many studies have shown that the only way to accurately gauge urine cortisol levels is to obtain the first morning voided urine sample on 3 consecutive days and then pooling the urine to run a UCCR. When done in this fashion it is likely an accurate test. Otherwise there is likely too much day to day variation to make a single random cortisol very helpful.
Dave Bruyette DVM DACVIM
To download the PDF, follow this link.
http://wvc.omnibooksonline.com/data/papers/2009_V101.pdf
Low Dose Dexamethasone Test (LDDS)
The protocol utilized for this test is obtaining plasma samples for cortisol before and 4 and 8 hours after I.V. administration of 0.01 mg/kg dexamethasone. The 8-hour plasma cortisol is used as a screening test for hyperadrenocorticism, with concentrations >1.4 μg/dl being consistent with (not confirming) the diagnosis of Cushing's syndrome. This test is relatively sensitive and specific, but not perfect. Approximately 90% of dogs with Cushing's syndrome have an 8 hour postdexamethasone
plasma cortisol concentration >1.4 μg/dl and another 6 to 8% have values of 0.9 - 1.3 μg/dl. The results of a low dose test can also aid in discriminating PDH from ACT, using three criteria: 1) an 8 hour plasma cortisol >1.4 μg/dl but <50% of the basal value; 2) a 4 hour plasma cortisol concentration <1.0 μg/dl; and 3) a 4 hour plasma cortisol concentration <50% of the basal value. If a dog has Cushing's and it meets any of these three criteria, it most likely has PDH. Approximately 65% of dogs with naturally occurring PDH demonstrate suppression, as defined by these three criteria. A dog with Cushing's that fails to meet any of these three criteria could have either PDH or ACT. However, if it has two relatively equal sized adrenals on abdominal ultrasonography, it most likely has PDH.
ACTH Stimulation (NO LONGER RECOMMENDED)
note: for diagnosing, that is....still the test to use to monitor a dog on treatment, tho)
The ACTH stimulation test has been popular for decades in veterinary medicine. It is simple to complete and takes little time. The other significant feature regarding results of an ACTH stimulation test is that this is the only study which reliably demonstrates the effect of o,p' DDD on the adrenal cortex. Thus, some veterinarians want results of an ACTH stimulation test, prior to initiating o,p' DDD therapy, because the results are used as “baseline” information to objectively monitor effects of o,p' DDD. Regardless of the protocol chosen, it must be appreciated that 20 - 30% of dogs with Cushing's syndrome have test results within the reference range (in our laboratory: post ACTH plasma cortisol concentrations of 6 to 17 μg/dl). An additional 20 - 30% of dogs with Cushing's have test results described as “borderline” (plasma cortisol concentrations >17 but <22 μg/dl). Therefore, the test is not considered sensitive but is relatively specific, i.e., those dogs with plasma cortisol concentrations >22 μg/dl frequently have Cushing's. However, specificity of an exaggerated response to ACTH is also not perfect. Therefore, test results should never be interpreted without knowing results of history, physical examination, and routine data base testing. There are no features of ACTH stimulation test result that allow discrimination between PDH and ACT. As ACTH has become more and more expensive, this test is losing popularity. .... In our opinion, the lack of sensitivity of the ACTH stimulation test makes it a test that the profession should abandon. The situations in which ACTH stimulation testing would be indicated include monitoring therapy for naturally occurring hyperadrenocorticism, to aid in the diagnosis of iatrogenic Cushing's syndrome, and as the “gold standard” for the diagnosis of naturally occurring hypoadrenocorticism (addison's disease).
Urine Cortisol: Creatinine Ratio (UC:CR)
The urine UC:CR ratio is easily performed (simply have the owner collect and deliver urine to the hospital and submit it to the laboratory) and, therefore, it is usually less expensive than other screening tests. Most dogs (~97%) with naturally occurring Cushing's syndrome have an abnormal result (the test is sensitive) but a significant percentage of dogs with polyuria / polydipsia due to other conditions and those with non-endocrine illness also have abnormal results (the test is not specific). It has been suggested that the UC:CR be routinely performed only on urine collected by an owner at home, rather than having it collected inhospital. Since this protocol eliminates travel or hospital stress from altering test results, it seems reasonable to follow this concept. We do not utilize this test with the same degree of confidence with which we use the low dose dexamethasone screening test. However, a normal result is quite uncommon in a dog with Cushing's syndrome while an abnormal result could be used to prompt further testing. Therefore, this test can be used as a prompt to recommend abdominal ultrasonography and a low dose dexamethasone test to an owner.
_________
Separately, Dr. Bruyette, an IM who specializes in endocrinology, discussed the need for a three-day pooled sample.
Urine cortisols can be a problem. Many studies have shown that the only way to accurately gauge urine cortisol levels is to obtain the first morning voided urine sample on 3 consecutive days and then pooling the urine to run a UCCR. When done in this fashion it is likely an accurate test. Otherwise there is likely too much day to day variation to make a single random cortisol very helpful.
Dave Bruyette DVM DACVIM
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