Endocrine Abstracts

Objectives: Secondary Adrenal Insufficiency is diagnosed using an ACTH stimulation test. There is no clear evidence that either a Low dose Synacthen Test (LDST) or a Short Synacthen Test is more superior in diagnosis. In our service, we routinely use LDST to investigate adrenal function. There is a lack of standardisation regarding timing, dose and frequency whilst undertaking a LDST leading to diagnostic inconsistencies. We routinely measure baseline cortisol levels, then at 10, 20, 30 and 60 minutes post Synacthen administration. Our aim was to evaluate whether we could rationalise the number of tests undertaken and in particular whether stopping the test at 30 minutes would be possible without misdiagnosing adrenal insufficiency.

Method: We undertook a retrospective analysis of all LDST results performed by our paediatric endocrine nurses in the last 10 years. Prior to January 2015 our cut off for diagnosing adrenal insufficiency was a maximum cortisol < 500 nmol/l; after 12th January 2015 the laboratory cortisol assay changed to being more sensitive and specific so our threshold reduced to < 450 nmol/l.

Results: 198 tests were analysed. 25% (50 out of 198) had a maximum cortisol level at 20 minutes, while 40% demonstrated this maximum level at 30 minutes (79 out of the 198). 30% of the cortisol levels peaked 60 minutes post the Synacthen dose. The rest were maximum at various other times. Since Jan 2015, 3 cortisol levels were maximum at 60 minutes. Of these, 2 were insufficient at 30 minutes but sufficient cortisol was attained by 60 minutes. In the same period, no test showed a maximum cortisol level at 10 minutes.

Conclusion: Analysing cortisol at 10 mins post synacthen did not aid the diagnosis of adrenal insufficiency and could safely be omitted from the protocol. Omitting the 60 min sample however would result in a number of children being diagnosed inappropriately with adrenal insufficiency. Although this would affect only a small proportion of individuals (2 out of 31), as the diagnosis has such important implications for management we would recommend that analysis of cortisol levels 60 min post synacthen is maintained.

Figure showing maximum cortisol levels at various times post synacthen dose