"It was pointed out that PPID is difficult to detect in its earliest stages, while advanced disease is relatively easy to recognize. The two most commonly used tests for PPID--resting adrenocorticotropin hormone( ACTH) concentrations and the overnight dexamethasone suppression test--can be used to confirm the diagnosis. However, these tests are less likely to yield positive results when PPID is first developing, so clinical judgment must be relied upon in these cases."
"New diagnostic tests are being developed for PPID and might allow earlier detection of the disorder. These include the combined dexamethasone suppression/thyrotropin-releasing hormone (TRH) stimulation test, TRH response test (with ACTH concentrations measured 10 and 30 minutes post-injection), and oral domperidone challenge test."