BTSC Staff Nurse 31 July-2025
Medical & Surgical Nursing
Easy
The overnight dexamethasone suppression test is primarily used to diagnose which of the following disorders?
Appeared in: BTSC Staff Nurse 31 July-2025
Explanation
- The overnight dexamethasone suppression test is a key screening procedure for Cushing syndrome.
- It works by testing the negative feedback mechanism of the hypothalamic-pituitary-adrenal (HPA) axis.
- In healthy individuals, dexamethasone (a synthetic steroid) suppresses the morning cortisol level.
- In patients with Cushing syndrome, the body's cortisol production is autonomous and is not suppressed by dexamethasone, leading to an elevated morning cortisol level.
- A plasma cortisol level that is not suppressed is a strong indicator of Cushing syndrome.
Why Other Options Were Wrong
- Option B: Thyrotoxic crisis is a life-threatening complication of hyperthyroidism. Its diagnosis relies on clinical presentation and thyroid function tests (e.g., TSH, free T4, and free T3), not on cortisol suppression.
- Option C: Myxoedema coma is a severe, life-threatening complication of hypothyroidism. Diagnosis is based on clinical signs and thyroid function tests that show very low thyroid hormone levels and typically an elevated TSH (in primary hypothyroidism).
- Option D: Marfan syndrome is a genetic disorder affecting the body's connective tissue. Diagnosis is made using a set of clinical criteria known as the Ghent nosology, which assesses features in the skeletal, ocular, and cardiovascular systems, along with family history and genetic testing.
Related Visual
Clinical Relevance
- Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Diagnostic screening for Cushing syndrome as background academic context rather than a clinical decision trigger.
- Early and accurate diagnosis of Cushing syndrome is crucial for nurses to understand, as it allows for timely treatment to prevent serious complications like hypertension, type 2 diabetes, osteoporosis, and increased susceptibility to infections.
- Nurses are responsible for patient education regarding the test, ensuring the patient understands to take the dexamethasone pill at the specified time and to return for the blood draw the next morning.
- A key nursing role involves monitoring patients with diagnosed Cushing syndrome for signs of complications and for the effectiveness of treatment.
How to Approach the Question
- First, identify the key procedure in the question: the 'overnight dexamethasone suppression test'.
- Recall the purpose of this test. Dexamethasone is a steroid, and the test involves 'suppression', which points to an endocrine feedback loop.
- Consider the hormone pathway being tested. Dexamethasone acts like cortisol to suppress the HPA axis. The test checks if this suppression works.
- Evaluate the options. Cushing syndrome is characterized by excess cortisol. The other options (thyroid crisis, myxedema, Marfan) are related to the thyroid or genetics, not the cortisol feedback loop.
- Conclude that the test is designed to identify autonomous cortisol production, which is the hallmark of Cushing syndrome.
Concept Tested & Keywords
- Concept Tested: Diagnostic screening for Cushing syndrome
- Stem keywords: overnight dexamethasone suppression test, diagnose, disorders
- Lead-in keywords: primarily used to diagnose
- Negative lead-in flag: false
Question ID
Qbg5ei2Vvh0Q3-fbxi0zuM
Reference Book
E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 1283-1285
E6 Robert Boland, Marcia L. Verduin - Kaplan and Sadock's Comprehensive Text of Psychiatry-Wolters Kluwer Health (2024) (pp 1-16525 of 16525) p. 7499-7501
E6 Ghai Essential Pediatrics(pp 26-904 of 913) p. 545-547
Practise the full BTSC Staff Nurse 31 July-2025
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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