Endocrine Abstracts

Does the dexamethasone-suppressed CRH test improve diagnostic accuracy in Cushing’s syndrome?

A Abdulali, NM Martin, WS Dhillo, A Banerjee, CN Jayasena, JF Todd & K Meeran

Hammersmith Hospital, London, United Kingdom.

The rising prevalence of obesity and type II diabetes makes the diagnosis of Cushing’s syndrome increasingly difficult. The dexamethasone-suppressed corticotrophin-releasing hormone (CRH) test, which involves CRH administration immediately following a standard low dose dexamethasone suppression test (LDDST), has been reported to diagnose Cushing’s syndrome with 100% sensitivity and specificity. We adapted our LDDST protocol to include CRH administration post-dexamethasone suppression. We investigated the diagnostic accuracy of this combined LDDST and CRH test (LDDST-CRH) and compared it to a standard LDDST by retrospectively studying 36 patients (including 12 confirmed cases of Cushing’s syndrome; 8 Cushing’s disease, 4 primary adrenal) who had undergone investigation for suspected Cushing’s syndrome.

The sensitivity of the standard LDDST in diagnosing Cushing’s syndrome was 100%, with a specificity of 88%. In contrast, although the LDDST-CRH diagnosed Cushing’s syndrome with 100% sensitivity, specificity was reduced at 67%. These results give a positive predictive value of 80% for the LDDST and 60% for the LDDST-CRH. Five subjects showed ‘discordant’ results whereby there was adequate suppression of serum cortisol following a standard LDDST, yet after CRH administration, serum cortisol exceeded the cut-off. Four subjects within this sub-group were amenable to repeat testing, and all subsequently ‘passed’ both the LDDST and LDDST-CRH tests without any intervention.

These data show that the combined LDDST-CRH test is less specific and accurate in the diagnosis of Cushing’s syndrome than was previously reported and does not improve the diagnostic accuracy of the LDDST.

Endocrine Abstracts (2005) 10 P77