Comparison of paired short Synacthen and insulin tolerance tests soon after pituitary surgery

The cortisol responses to hypoglycaemia (insulin tolerance test, ITT) and tetracosactrin (short Synacthen test, SST) were compared after hypophysectomy to evaluate the SST for the assessment of hypothalamo-pituitary-adrenocortical (HPA) axis function in the immediate post-operative period. In 12 patients who were tested a mean of 21 months postoperatively (range 1-96) peak plasma cortisol in the SST correlated with that in the ITT (r = 0.90). Correlation was also seen in 12 patients tested a mean of 9 days (range 4-18) after hypophysectomy (r = 0.73). Basal-peak cortisol increments did not correlate. The peak plasma cortisol response in each test was classified by comparison with a reference value of 550 nmol/L. On this basis there was a notable discrepancy between the ITT and SST results in only one patient who was tested 4 days after hypophysectomy. The close correlation between ITT and SST responses after pituitary surgery extends into the immediate post operative period and indicates that the latter test can be used to screen HPA axis function at this time.