Introduction: Traditionally the long synacthen test (LST) is used in some centres to assess hypothalamic/ pituitary and adrenal (HPA) axis. Evidence that it offers advantage over short synacthen test (SST) is lacking. Whilst changing our local protocol we evaluated 27 patients who had both tests in our trust. We compared the impact of the results in clinical decision making.
Results: Mean age was 53 years. The indications for the tests were assessment for long term steroid induced hypoadrenalism (16), post pituitary surgery (6), post unilateral adrenalectomy (3), and other reasons (2). The cut off value for 30 min rise in cortisol was taken as 500 nmol/L in SST and peak cortisol response at 48 hours in LST was taken as 900 nmol/L. A recent assay change in cortisol measurement in our lab was applied to both the values (20% reduction). 12 patients (44%) had evidence for adrenal suppression on SST and 14 (51%) on LST. 2 patients had a good response on SST although but suppression on LST subsequently giving false negative/non-concordance rate of 7%. 3 patients had delayed response with peak at 24 hours which usually occurs in secondary adrenal failure. All 3 were being assessed for long term steroid induced hypoadrenalism and they also had evidence of adrenal suppression on SST. Overall there was good correlation between the SST and LST results.
Conclusion: There is considerable evidence for SST that it is an effective test to assess HPA axis. For clinical decision making SST is simple, cost effective, less laborious and reliable test.