Two Tests for the Differential Diagnosis of Cushing’s Disease and Pseudo-Cushing’s

close up of scientist with test sample making research in clinical laboratoryResearchers examined two diagnostic tests for Cushing’s disease: the corticotropin-releasing hormone (hCRH) and desmopressin (DDAVP) tests.  These tests are used for the differential diagnosis of Cushing’s disease (CD) and pseudo-Cushing’s disease (PC).

Their study was published in the November 2011 issue of Clinical Endocrinology (Oxford). It was entitled “Corticotrophin-releasing hormone and desmopressin tests in the differential diagnosis between Cushing’s disease and pseudo-Cushing state: a comparative study.”

The researchers were mainly concerned with this question:  is performing both tests more beneficial than doing just one of the tests?

To attempt to answer this question, the researchers studied 30 patients with CD, 18 with PC, and 12 control subjects (CT).  All the subjects had the following done:

  • hCRH test
  • DDAVP test
  • 24 hour urinary free cortisol
  • serum cortisol after overnight 1-mg dexamethasone suppression test
  • serum cortisol circadian rhythm

The researchers found that the DDAVP and hCRH tests demonstrated identical and excellent diagnostic performance.  For both tests, the sensitivity was 96.6% and the specificity was 100%.

Additionally, the test had almost perfect diagnostic agreement (k=0.93; p < 0.05).  They had a significantly higher number of concordant diagnosis—58 out of 60 cases—than those from any other combination of the tests used.

It is noted that the hCRH and DDAVP tests never gave a simultaneous misdiagnosis.

In conclusion, the hCRH and DDAVP have similar diagnostic performance; they also have excellent agreement and do not give simultaneous misdiagnosis.  Therefore, the tests are a valuable tool for physicians to use if they have a case of hypercortisolism that is hard to interpret.

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