II. Indications: Cushing's Syndrome Screening
- Preferred test if adrenal tumor suspected or Night Shift Worker (altered circadian rhythm)
- Among 3 first line options for Cushing's Syndrome Screening
- See 24-hour Urinary Free Cortisol level
- See Late-Night Salivary Cortisol (LNSC)
III. Mechanism
- Test measures Adrenal Gland response to ACTH
- ACTH should decrease in response to Dexamethasone
- Decreased ACTH should result in decreased Cortisol
- Failure for Cortisol to suppress suggests 2 causes
- Pituitary GlandACTH over-produced or
- Adrenal GlandCortisol over-produced
IV. Protocol
- Step 1: Patient takes Dexamethasone 1 mg at 11 pm on day 1
- Step 2: Draw Serum Cortisol at 8-9 am on day 2
V. Interpretation (Based on 8 am Serum Cortisol on day 2)
- AM Serum Cortisol <5 mcg/dl (especially if <1.8 mcg/dl)
- Normal response (Suppresses)
- AM Serum Cortisol >5 mcg/dl
- Cushing's Disease
- Repeating with Dexamethasone 8 mg determines site
- Adrenal Gland source will not suppress
- Pituitary source will suppress
VI. Causes: False Positives
- Increased gastrointestinal transit (e.g. Diarrhea)
- Pseudo-Cushing's Syndrome
-
CYP3A4 Inducers (increase Dexamethasone metabolism)
- Neuropsychiatric drugs (Carbamazepine, Phenobarbital, Phenytoin,St. John's Wort)
- Rifampin
- Troglitazone
-
Corticosteroid Binding Globulin increased
- Pregnancy
- Estrogen
- Chronic hepatitis
VII. Causes: False Negatives
- Hepatic Impairment
- Renal Impairment (eGFR<60 ml/min)
- Hypoalbuminemia
- Corticosteroid Binding Globulin decreased
- CYP3A4 Inhibitors (decrease Dexamethasone metabolism)
VIII. Efficacy
- Some protocols recommend a 3 stage Dexamethasone test for higer Test Sensitivity
- Draw Serum Cortisol at 4 pm on day 1 before Dexamethasone
- Accuracy is also improved when Dexamethasone level is checked on day 2 (in addition to Cortisol)
- Low-Dose Dexamethasone Suppression Test
- Test Sensitivity: 85 to 90%
- Test Specificity: 95 to 99%
- Strong Negative Predictive Value
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Related Studies
| Definition (PSY) | Laboratory analysis of hypersecretion of cortisol and the body's failure to suppress cortisol after the administration of dexamethasone. Used primarily for diagnosis of major depressive disorders. |
| Definition (CSP) | injection of dexamethasone causes serum cortisol to fall; this can be correlated with behavioral measures of depression, but the test is not reliable enough for diagnostic use. |
| Concepts | Laboratory Procedure (T059) |
| SnomedCT | 392884002, 393839005, 252190006 |
| Italian | Test di soppressione con desametasone |
| English | Dexamethasone suppression test, DST, dexamethasone suppression test, dexamethasone suppression tests, dst, Dexamethasone suppression test (procedure), Dexamethasone Suppression Test |
| Czech | Dexametazonový supresní test |
| Hungarian | Dexamethason suppressziós vizsgálat |
| Japanese | デキサメタゾン抑制試験, ﾃﾞｷｻﾒﾀｿﾞﾝﾖｸｾｲｼｹﾝ |
| Spanish | prueba de supresión con dexametasona (procedimiento), prueba de supresión con dexametasona, Prueba de supresión con dexametasona |
| Portuguese | Exame de supressão de dexametasona |
| Dutch | dexamethason-suppressietest |
| French | Épreuve de freinage à la dexaméthasone |
| German | Dexamethason-Suppressionstest |
Ontology: Low dose dexamethasone suppression test (C0430116)
| Concepts | Laboratory Procedure (T059) |
| SnomedCT | 252191005 |
| English | Dexamethasone Test Low Dose Suppression, Low dose dexameth supp test, Low dose dexamethasone suppression test, Low dose dexamethasone suppression test (procedure) |
| Spanish | prueba de Liddle a dosis bajas, prueba de supresión con dexametasona a dosis bajas (procedimiento), prueba de supresión con dexametasona a dosis bajas |
