Background: Cushings disease is the most common cause of endogenous Cushings syndrome in adults, affecting females>males (ratio 3:1). In suspected cases, careful clinical assessment is required to ascertain a pre-test probability. This is followed by robust biochemical testing, which guides further management.
One-week test protocol: Congruent biochemical tests are conducted over a one-week period in an outpatient setting. Patients attend on day 1, bringing two 24 h urine collections for measurement of urinary free cortisol (UFC), and two late-night salivary cortisol (LNSC) samples, collected during the preceding 48 h. On day-1, a serum cortisol day profile is performed with LNSC to assess the diurnal rhythm. Plasma adrenocorticotrophic hormone (ACTH) is also checked at 0900 h. On the second day, at 0900 h, anterior pituitary function tests (including repeat ACTH) are performed, followed by the commencement of a low dose dexamethasone suppression test (Table 1). Patients receive instructions on the appropriate method/technique for performing each test. Patients symptoms, medications and basic observations are recorded.
Key: ACTH, adrenocorticotrophic hormone; CDC, cortisol day curve; LDDST, low dose dexamethasone suppression test; LNSC, late-night salivary cortisol; UFC; urinary free cortisol.
Illustrative case An 18-year-old lady with mild learning-difficulty presented with clinical features of Cushings syndrome. Outpatient investigation (with close instructions regarding test methodology and sample collection techniques) was undertaken. Results confirmed pituitary-dependent Cushings. Transsphenoidal adenomectomy was successful in rendering the patient in complete remission (hydrocortisone dependent) with no other pituitary deficits.
|Patients home||Endocrine unit (outpatient visits)|
|UFC||UFC||CDC, ACTH||0900 h pituitary profile, ACTH||Continue LDDST||0900 h cortisol|
Conclusion: Accurate sample collection, timing and labelling is a crucial step in the correct interpretation of Cushings investigations. Focussed one-week testing allows better instruction delivery by the endocrine nurse.