{"id":1288165,"date":"2022-03-06T23:20:36","date_gmt":"2022-03-07T04:20:36","guid":{"rendered":"https:\/\/myendoconsult.com\/learn\/?p=1288165"},"modified":"2023-06-07T22:13:09","modified_gmt":"2023-06-08T03:13:09","slug":"dexamethasone-suppression-test-interpretation","status":"publish","type":"post","link":"https:\/\/myendoconsult.com\/learn\/dexamethasone-suppression-test-interpretation\/","title":{"rendered":"Dexamethasone Suppression Test Interpretation"},"content":{"rendered":"

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What is the Dexamethasone Suppression Test (DST)?<\/b><\/p>\n

The original protocol for assessing Cushing\u2019s syndrome was first described in the 1960s. Liddle\u2019s protocol involves the sequential administration of low-dose dexamethasone followed by high dose dexamethasone in patients with suspected endogenous hypercortisolemia.<\/p>\n

Effect of Dexamethasone on the Hypothalamic-Pituitary-Adrenal (HPA) axis<\/h2>\n

Dexamethasone is the most potent exogenous glucocorticoid (up to 15x more potent than hydrocortisone) and exerts profound negative feedback inhibition of the HPA axis. More importantly, it does not bind cortisol-binding globulin, a property that allows it to traverse the blood-brain barrier easily.<\/p>\n

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Dexamethasone has no cross-reactivity with hydrocortisone and its metabolites, as such is not measurable in the standard cortisol immunoassay. This makes it an ideal exogenous glucocorticoid for dynamic testing<\/a> of the HPA axis.<\/p>\n<\/blockquote>\n

Procedure and interpretation of the 1mg dexamethasone suppression test<\/h2>\n\n\n\n\n\t\n\t\n\t\n\t
DST<\/td>Comments<\/td>\n<\/tr>\n
Procedure<\/td>\u2022\tAdminister 1mg of dexamethasone b\/n 2300-2400h
\n\u2022\tSampling of serum cortisol b\/n 0800-0900h
\n<\/td>\n<\/tr>\n
Rationale <\/td>\u2022\tDexamethasone is administered between 2300 and 2400h to inhibit the ACTH secretion, which starts at 0300h and peaks by 0700h<\/td>\n<\/tr>\n
Interpretation<\/td>\u2022\tThe cutoff for diagnosing endogenous hypercortisolemia is > 1.8 \u03bcg\/dl with a sensitivity of 95% and a specificity of 80%.
\n\u2022\tThe HPA axis recovers within 24 h after the administration of a single dose of 1 mg dexamethasone.
\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n

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Drugs interfering with Dexamethasone Suppression Test<\/h2>\n

A thorough drug history is required to exclude excessive exogenous glucocorticoid exposure (leading to iatrogenic Cushing\u2019s syndrome<\/a>) before conducting biochemical testing<\/p>\n

Causes of a false positive DST<\/strong><\/p>\n\n\n\n\n\t\n\t\n\t\n\t\n\t
Category<\/td>Causes<\/td>\n<\/tr>\n
Pseudo-Cushing\u2019s syndrome <\/td>Depression, alcoholism, pregnancy, chronic kidney disease, glucocorticoid resistance syndrome, and acute stress<\/td>\n<\/tr>\n
Medications associated with an increase dexamethasone metabolism <\/td>Rifampicin, phenytoin, phenobarbitone, carbamazepine, and pioglitazone <\/td>\n<\/tr>\n
Medications associated with an increase in CBG <\/td>Estrogen, mitotane, and tamoxifen.<\/td>\n<\/tr>\n
Unpredictable intra-individual variation <\/td>Variation in absorption and metabolism of dexamethasone can also result in false- positive DST **<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n

** For this reason, assessing serum dexamethasone in addition to cortisol levels is required to detect this.<\/em><\/p>\n

Causes of a false negative DST<\/strong><\/p>\n\n\n\n\n\t\n\t\n\t\n\t
Category<\/td>Causes<\/td>\n<\/tr>\n
Intermittent hypercortisolemia<\/td>Cyclical Cushing\u2019s syndrome<\/td>\n<\/tr>\n
Iatrogenic exposure to steroids<\/td>Exogenous Cushing\u2019s syndrome<\/td>\n<\/tr>\n
Inhibition of the metabolism of dexamethasone <\/td>Ritonavir, itraconazole, cimetidine, fluoxetine, and diltiazem<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n

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When is Dexamethasone Suppression Test Required?<\/h2>\n