Endocrine Abstracts

Introduction: Misdiagnosis of secondary hypocortisolaemia can have profound consequences on a patient’s life. Due to contraindications the gold standard dynamic diagnostic test of cortisol reserve – the insulin tolerance test (ITT) – may not always be suitable. Here we examine the diagnostic accuracy of the second line dynamic tests: the overnight metyrapone test (OMT), short synacthen test (SST) and glucagon stimulation test (GST).

Patients and methods: Retrospective collection of records of dynamic testing of cortisol in patients with suspected ACTH deficiency from two tertiary care centres for pituitary disease. The ITT was used as the reference method for comparison using a cortisol threshold value of 450 nmol/l. 119 patient records were collected, 83 being investigated for pituitary disease, 29 post-TBI and seven classified as other. Comparison of the ITT with the OMT, SST and GST was possible in 45, 37 and 26 individuals respectively.

Results: 47% showed a suboptimal cortisol response on ITT. The SST demonstrated the greatest concordance with the ITT (64%) followed by the OMT (63%) and GST (36%). ROC analysis revealed an optimum cut-off of 550 nmol/l for the SST with a sensitivity of 75% and specificity of 63%, and 200 nmol/l 11-deoxycortisol for the OMT with a sensitivity of 58% and specificity of 73%.

Conclusion: The SST offers the best assessment of cortisol reserve against the ITT, but given the associated high false negative rate, the threshold value may need to be adjusted to a higher value of 550 nmol/l before the SST surpasses the OMT as the preferred second line test behind the ITT.