Aim: This study was aimed to assess the need for multiple cortisol samples in ruling out adrenal insufficiency by standard dose Short Synacthen Tests (SST) and Low Dose Short Synacthen Tests (LDSST).
Method: We assessed the lab results of 767 patients who attended Metabolic Unit of a University Hospital in the UK from 1999 to 2006 for assessment of adrenal reserve. In LDSST, serum cortisol was measured at 0, 30 and 40 min after administration of 1 mcg of synacthen and in SST; these measurements were done at 0, 30 and 60 min after 250 mcg of synacthen. The response of cortisol level of 550 was considered adequate to rule out adrenal insufficiency and data was analysed to ascertain the proportion of patients who achieved this level at 30 min.
Results: 391 Patients had LDSST. 245 patients achieved peak level of 550 and in majority of these patients (n 237, 96.74%) peak levels were achieved at 30 min. 146 patients failed to achieve peak levels at 30 as well as 40 min samples.
376 Patients had SST. 351 patients achieved level of 550 at 60 min. Majority of these patients (n: 335, 95.45%) achieved this level at 30 min. 23 patients failed SST and in all these patients 30 min level was below 500.
Summary: For ruling out adrenal insufficiency, 40 or 60 min level did not add a lot in 96% patients.
Conclusion: Doing multiple timed cortisol assays does not add a lot and 30 min level is sufficient to interpret standard dose as well as low dose short synacthen tests.