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Dexamethasone Suppression Test (DST), 1 Specimen
Test Code6921
CPT Codes
82533
Preferred Specimen
1 mL serum
Minimum Volume
0.5 mL
Instructions
The ordering physician should administer 1 mg Dexamethasone between 11:00 p.m. and midnight. Draw serum for cortisol testing between 7:00-9:00 a.m. the next morning. Mark tube with time and date drawn.
Note: Dexamethasone not supplied by the laboratory.
Note: Dexamethasone not supplied by the laboratory.
Transport Temperature
Room temperature
Specimen Stability
Room temperature: 7 days
Refrigerated: 7 days
Frozen: 28 days
Refrigerated: 7 days
Frozen: 28 days
Methodology
Immunoassay (IA)
Setup Schedule
Set up: Mon-Sun; Report available: Next day
Reference Range
For 8 a.m. Specimen:
Further diagnostic tests must be performed to confirm the diagnosis and determine etiology. Values >1.8 mcg/dL mcg/dL can also be seen in endogenous depression and other forms of endogenous hypercortisolism (also known as pseudo-Cushing) such as pregnancy, severe obesity, psychological stress, and chronic alcoholism especially during withdrawal.
CKD: The low-dose DST can be used in patients with CKD if the post-DST morning cortisol cutoff is adjusted for the degree of impaired kidney function.
Pregnancy: The low-dose 1 mg overnight DST is not mcg/dL recommended to diagnose Cushing syndrome during pregnancy, because of the risk of false-positive results.
Drugs: Drugs that induce hepatic CYP3A4 enzymes, such as mcg/dL barbiturates, phenytoin, rifampin, and carbamazepine, increase the metabolism of dexamethasone and affect its level.
| <1.8 mcg/dL | Normal response |
| 1.8-10.0 mcg/dL | Equivocal |
| >10.0 mcg/dL | High probability of Cushing's syndrome |
Further diagnostic tests must be performed to confirm the diagnosis and determine etiology. Values >1.8 mcg/dL mcg/dL can also be seen in endogenous depression and other forms of endogenous hypercortisolism (also known as pseudo-Cushing) such as pregnancy, severe obesity, psychological stress, and chronic alcoholism especially during withdrawal.
CKD: The low-dose DST can be used in patients with CKD if the post-DST morning cortisol cutoff is adjusted for the degree of impaired kidney function.
Pregnancy: The low-dose 1 mg overnight DST is not mcg/dL recommended to diagnose Cushing syndrome during pregnancy, because of the risk of false-positive results.
Drugs: Drugs that induce hepatic CYP3A4 enzymes, such as mcg/dL barbiturates, phenytoin, rifampin, and carbamazepine, increase the metabolism of dexamethasone and affect its level.
Clinical Significance
Cortisol is increased in Cushing's Disease and decreased in Addison's Disease (Adrenal insufficiency).
