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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). Emerging data has demonstrated that patients with difficult-to-treat Type II Diabetes (HbA1c >7.5% despite medication) may also have elevated cortisol levels, akin to Cushing's Disease; however, the physical manifestations are not as obvious, and prevalence is significantly higher.
1. Buse JB, Kahn SE, Aroda VR, et al. Prevalence of hypercortisolism in difficult-to-control type 2 diabetes. Diabetes Care. 2025;48(12):2012-2020 doi: 10.2337/dc24-2841
2. DeFronzo RA, Auchus RJ. Cushing Syndrome, hypercortisolism, and glucose homeostasis: a review. Diabetes. 2025;74(12):2168-2178. doi: 10.2337/db25-0120
3. Lundqvist MH, Pereira MJ, Almby K, et al. Regulation of the cortisol axis, glucagon, and growth hormone by glucose is altered in prediabetes and type 2 diabetes. J Clin Endocrinol Metab. 2024;109:e675-e688. doi: 10.1210/clinem/dgad549
4. Nieman LK, Biller BMK, Findling JW, et al. The diagnosis of Cushing's Syndrome: an endocrine society clinical practice guideline. J Clin Endocrinol Metab. 2008; 93: 1526-1540. doi: 10.1210/jc.2008-0125
5. DeFronzo RA, Fonseca V, Aroda VR, et al. Inadequately controlled type 2 diabetes and hypercortisolism: improved glycemia with mifepristone treatment. Diabetes Care. 2025;48(12):2036-2044. doi: 10.2337/dc25-1055
1. Buse JB, Kahn SE, Aroda VR, et al. Prevalence of hypercortisolism in difficult-to-control type 2 diabetes. Diabetes Care. 2025;48(12):2012-2020 doi: 10.2337/dc24-2841
2. DeFronzo RA, Auchus RJ. Cushing Syndrome, hypercortisolism, and glucose homeostasis: a review. Diabetes. 2025;74(12):2168-2178. doi: 10.2337/db25-0120
3. Lundqvist MH, Pereira MJ, Almby K, et al. Regulation of the cortisol axis, glucagon, and growth hormone by glucose is altered in prediabetes and type 2 diabetes. J Clin Endocrinol Metab. 2024;109:e675-e688. doi: 10.1210/clinem/dgad549
4. Nieman LK, Biller BMK, Findling JW, et al. The diagnosis of Cushing's Syndrome: an endocrine society clinical practice guideline. J Clin Endocrinol Metab. 2008; 93: 1526-1540. doi: 10.1210/jc.2008-0125
5. DeFronzo RA, Fonseca V, Aroda VR, et al. Inadequately controlled type 2 diabetes and hypercortisolism: improved glycemia with mifepristone treatment. Diabetes Care. 2025;48(12):2036-2044. doi: 10.2337/dc25-1055
