HDDST &LDDST are equally important to access Adrenocortical insufficiency
HDDST (high-dose dexamethasone suppression test)
Procedure
• 2 mg
dexamethasone
6-hourly for 48 hrs
• To measure 24-hr urine cortisol at baseline and during second day
• It is important for any oestrogens (OCP) to be stopped for 6 weeks prior to investigation to allow corticosteroid-binding globulin (CBG) levels to return to normal and to avoid false-positive responses, as most cortisol assays measure total cortisol, including that bound to CBG.
• Other Steroids, adrenal enzyme inhibitors, statins and carbamazepine must be discontinued prior to testing.
Interpretation
• It is done after positive CRH test in case of raised plasma ACTH.
• If > 50% suppression (of serum cortisol) from baseline à Cushing’s disease (Suggestive)
LDDST (low-dose dexamethasone suppression test)
Procedure
• Administration of 0.5 mg dexamethasone 4 times daily (Eight doses) for 48 hours.
• 0900-hr plasma cortisol on days 0 and after 48 hrs
• It is important for any oestrogens (OCP) to be stopped for 6 weeks prior to investigation to allow corticosteroid-binding globulin (CBG) levels to return to normal and to avoid false-positive responses, as most cortisol assays measure total cortisol, including that bound to CBG.
• Other Steroids, adrenal enzyme inhibitors, statins and carbamazepine must be discontinued prior to testing.
Normal value
SI
50 nmol/L
CU
1.81 μg/dL
Interpretation
• Normal individuals suppress plasma cortisol to <50 nmol/L.
• In Cushing’s syndrome it fails to show complete suppression of plasma cortisol levels
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