Dexamethasone Suppression Test (DST), 1 Specimen
- Laboratory
- Quest Diagnostics
- Test code
- 6921
- Specimen
- Serum
- Fasting
- Not stated
- LOINC
- 1434-0
Laboratory assay overview
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
Quest Diagnostics population reference ranges
Quest Diagnostics calculates these statistical intervals for this specific assay and demographic group, not as universal optimal targets.
| Population | Range |
|---|---|
| <1.8 mcg/dL | Normal response |
| 1.8-10.0 mcg/dL | Equivocal |
| >10.0 mcg/dL | High probability of Cushing's syndrome |
View complete laboratory reference notes
For 8 a.m. Specimen: <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.
Quest Diagnostics test directory, test code 6921