Background: The short synacthen test (SST) is the most commonly performed investigation to assess for suspected adrenocortical dysfunction. We investigated how random cortisol levels may relate to pass/fail on the STT.
Methods: We analysed the relation between random cortisol measurements taken between 04.40 and 20.52 in the day and results of SST baseline and 30/60 min cortisol performed over a 12 month period (338 SSTs) at Salford Royal Hospital. Serum cortisol was measured on the Siemens Centaur Autoanalyser (Erlangen, Germany). A 30/60 minute cortisol of ≥500 nmol/l in the presence of a baseline of ≥200 nmoll was taken as a pass. Failure of cortisol to reach 350 nmol/l post-Synacthen was taken as a definite fail.
Results: The findings indicate that a random cortisol level of ≥195nmol/l is associated with a pass on the STT in 100% of cases. A random cortisol level of 95 nmol/l or less was associated with a fail on the STT in 100% of cases. Overall there was no significant relation between random cortisol and 30 min post-Synacthen cortisol. In relation to the agreed pass cut off post-Synacthen of cortisol ≥500 nmol/l, in 8.5% of cases the 60 min cortisol was ≥500 nmol/l but 30 min cortisol was below. Thus the 60 min cortisol indicated adequate adrenocortical function. In 0.5% of cases the converse was true. For a definite fail of cortisol <350 nmol/l there was disagreement between 30 and 60 min cortisol in 10 cases. In 30% of these cases the 60 minute cortisol was ≥350 nmol/l but the 30 min cortisol was below 350 nmol/l. In other words.
Conclusion: Our findings suggest that in the if the random cortisol level is ≥195 nmol/l, there may be no need to perform a SST unless specific evaluation is required. In 8.3% of cases an adequate cortisol response was seen at 60 min but not at 30 min. The 60 min cortisol therefore retains utility.