SHORT SYNACTHEN TEST 250µg FOR EVALUATION OF HYPOTHALAMIC PITUITARY ADRENAL AXIS IN LONG-TERM GLUCOCORTICOID USERS
Background: Long-term glucocorticoid therapy can result in suppression of hypothalamic-pituitary-adrenal (HPA) axis. Before glucocorticoid is stopped, secondary adrenal insufficiency should be assessed by provocative test. Objectives: To assess the usefulness of short synacthen (STT) 250µg in diagnosing secondary adrenal insufficiency in long-term glucocorticoid users before withdrawal of glucocorticoid, compared with insulin hypoglycemia test (IHT) as reference test.
Methods: Cross sectional study was performed at People Hospital 115, Ho Chi Minh City from 2/2009 to 4/2011. Long-term glucocorticoid users on low dose of glucocorticoid had STT 250µg and IHT performed on 2 separate days. Hypothalamic pituitary adrenal axis suppression was defined as maximal plasma cortisol in IHT equal or less than 18µg/dL. The IHT was used as the 'gold standard' in assessing the HPA axis. Results: 70 patients (64% female) had mean age of 36±12 years. Adrenal insufficiency was confirmed in 68.6% (48/70 patients). During STT, mean plasma cortisol level at 0 min, 30 min and 60 min was 8.0±4.4µg/dL, 18.2±7.9µg/dL, 20.4±9.0µg/dL, respectively. Maximal plasma cortisol was significantly higher in STT than this in IHT (20.6±8.9µg/dL vs 15.3±6.5µg/dL, p=0.0001). There was significant correlation between maximal plasma cortisols in STT and in IHT r=0.78 (95% CI 0.66–0.85), p<0.001). Synacthen test was used for diagnosis of HPA supression with area under ROC curve of 0.89 (95% CI: 0.79-0.95; p=0.0001). For diagnosis of secondary adrenal insufficiency, maximal plasma cortisol cut off at 23.9µg/dL had sensitivity of 89.6% and specificity of 72.7%.
Conclusions: Maximal plasma cortisol value of 23.9µg/dL as cut-off in short synacthen test (250µg) is valid test for assessing HPA axis function in long-term glucocorticoid users. Key words: Basal plasma cortisol, adrenal insufficiency, short synacthen test, insulin hypoglycemia test.