Endocrine Abstracts (2006) 11 P549

Diagnostic utility of dexamethazone suppression tests in the work-up of Cushing’s disease

EJ Roderick, K Collison, N Karavitaki, HE Turner, S Suliman & JAH Wass


Department of Endocrinology, Oxford Centre for Diabetes, Endocrinology and Metabolism, Oxford, United Kingdom.


Background: Cushing’s disease (CD) may be associated with equivocal results on biochemical investigations.

Aim: To evaluate the usefulness of dexamethazone suppression tests in the diagnostic work-up of CD.

Patients and methods: Seventy patients with CD [median age 38 yrs(16–76), 53 females] presenting between 1976–2005 were studied. 24-hr urinary free cortisol (UFC), overnight (oDST) (1 mg at 23:00 h), low dose (LDDST) (2 mg daily over 2 days), high dose (HDDST) (8 mg daily over 2 days) dexamethasone suppression tests were assessed. Statistical analyses were based on subjects with available data on each occasion.

Results: At initial evaluation 96.4%(53/55) had UFC above normal [median 674 nmol/24 hr(195–5220)]. Failure of suppression of serum cortisol (<50 nmol/l) was found in 0%(0/30) on the oDST [median 465 nmol/l(151–1396)] and 97.7%(42/43) on the LDDST [median 346 nmol/l(49–899)]. 29.2%(14/48) suppressed serum cortisol <50% on the HDDST [median 81.7%(0–92.7%)]. There was no difference in the UFC among subjects suppressing serum cortisol >50% or <50% on HDDST (median 597 vs 1620 nmol/24 hr, P=0.2). There was significant correlation between UFC and serum cortisol on oDST (r=0.6, P=0.04), serum cortisol on LDDST (r=0.5, P=0.03), but not percentage fall of serum cortisol on HDDST (P=0.09). No significant correlation between percentage fall of serum cortisol on the HDDST and serum cortisol values on the oDST (P=0.1) or on the LDDST (P=0.1) was found. There was a significant correlation between the percentage fall of serum cortisol on the LDDST and the HDDST (48hours) (r=0.4, P=0.03).

Conclusions: In our series, the LDDST was overall satisfactory for the diagnosis of hypercortisolism. The HDDST showed high rate of false negative results rendering it unsatisfactory in the diagnostic work-up of CD. The correlation between percentage fall of serum cortisol on the LDDST and HDDST suggests that the LDDST may be useful in predicting the pituitary origin of Cushing’s syndrome.

Article tools

My recent searches

No recent searches.