Comparison of Paired Short Synacthen and Insulin Tolerance Tests Soon after Pituitary Surgery

Abstract

SUMMARY. 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=0·9O). Correlation was also seen in 12 patients tested a mean of 9 days (range 4-18) after hypophysectomy (r = O' 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 nmollL. 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. Additional key phrases: hypophysectomy; function; hypoglycaemia; tetracosactrin; cortisolPituitary surgery can cause inadequacy of adrenocorticotrophic hormone (ACTH) secretion and secondary hypocortisolism. Patients are tested to identify those who need replacement therapy. The insulin tolerance test (ITT) is regarded as the standard test of hypothalamo-pituitaryadrenocortical (HPA) axis function. It is inconvenient and potentially dangerous and not beyond criticism. The safer and simpler short Synacthen test (SST) directly tests adrenocortical function and indirectly also assesses integrated HPA axis function on the basis that deficiency of endogenous ACTH causes involution of the adrenal cortex and reduced response to exogenous ACTH. 1The adrenocortical response to exogenous ACTH has been shown to correlate closely with that to surgical and hypoglycaemic stress.':"The ITT and SST results might be expected to differ in circumstances of acute impairment of Correspondence: Dr R S Jackson, Department of Chemical Pathology, The Ipswich Hospital, Heath Road, Ipswich, Suffolk IP4 SPD, UK. 46ACTH secretion, for example after hypophysectomy, if performed before adrenocortical function has declined. However, the time lag for reduction of adrenocortical responsiveness in the SST secondary to acute reduction of ACTH may be short" and direct comparison of SST and ITT has not been made close to this time, for example after pituitary surgery. Accordingly, the ITT is still frequently used in the immediate postoperative period to determine the need for cortisol replacement therapy. The possibility of using the SST instead is attractive? and indeed the SST has been performed as early as 8 days postoperatively, but without ITT for comparison." A larger study of paired SSTs and ITTs excluded patients within 15 days of pituitary surgery." The aim of this study was to compare the results of paired SSTs and ITTs in this immediate postoperative period. PATIENTS AND MET...

Comparison of one week 0900 h serum cortisol, low and standard dose Synacthen tests with a 4 to 6 week insulin hypoglycaemia test after pituitary surgery in assessing HPA axis

“…Indeed in studies of patients following pituitary surgery worrying discrepancies between the tests have been identified. (Jackson et al ., 1994; Mukherjee et al ., 1997).…”

Comparison of tests of stress‐released cortisol secretion in pituitary disease

“…It assumes that in hypopituitarism the adrenal cortex atrophies due to chronic corticotrophin deficiency and therefore cannot respond to an acute dose of exogenous corticotrophin. It is said to be unreliable within 14 days of pituitary insult such as surgery or infarction (Lindholm & Kehlet, 1987;Jackson et al, 1994) or in patients taking oral corticosteroids (Clayton, 1989;Harrison et al, 1982).…”

The insulin hypoglycaemia test for the assessment of the hypothalamic–pituitary–adrenal function

“…Its physiological mechanism appears simple and straightforward. A major disadvantage is its well‐known inability to identify HPA insufficiency shortly after corticotrophin deprivation (Hjortup et al , 1983; Jackson et al , 1994). It has been advocated that if the outcome of the short ACTH test is borderline or ambiguous, further testing should be undertaken, in most cases an additional IHT being the preference.…”