administered overnight indicates normal suppression of the hypothalamic pituitary adrenal axis. A morning cortisol nmol/L after 1 mg dexamethasone administered Abnormal 1mg DST ≥ 50 overnight suggests hypercortisolism. False positive responses non-compliance, malabsorption, drugs inducing the hepatic – metabolism of dexamethasone (phenytoin, carbamazepine, phenobarbital, rifampicin), drugs elevating CBG (oestrogens), chronic kidney disease, acute illness and pseudo-Cushing’s (depression, alcohol abuse, eating disorders). False negative responses nephrotic syndrome renal dialysis, chronic liver disease – (↓CBG), (reduced metabolism and clearance of dexamethasone). Sensitivity 98-100%, Specificity 85% NOTES: 25% of hospitalised inpatients will have an abnormal 1 mg dexamethasone suppression test, if possible, investigations should be delayed until acute illness has subsided. 2.2 LATE NIGHT SALIVARY CORTISOL PREPARATION & PROCEDURE: Patient to collect Salivettes from clinic or laboratory collection centre. Patient should chew on Salivette for 2 minutes (or until saturated with saliva) between 11pm to midnight prior to brushing their teeth, and not within 30 mins of eating or drinking. Minimum of two separate samples should be collected. Salivary cortisol is stable at room temperature. Patient should drop or post Salivettes back to laboratory collection centre. Smokers should avoid cigarette smoking on the day of the test. Time Procedure Comment 11pm Chew on salivette provided for Collect prior to brushing teeth and nil by minutes until saturated. mouth for at least 30 mins prior to collection. INTERPRETATION: Normal response Consult reference intervals provided by the laboratory. – smokers and especially patients who chew tobacco, False positive responses – contamination of salivettes with corticosteroid, bleeding of the gum, shift workers. False negative responses - non-compliance with collection procedure (drinking water dilutes the sample), cyclical Cushing’s.
administered overnight indicates normal suppression of the hypothalamic pituitary adrenal axis. Abnormal 1mg DST A morning cortisol ≥ 50 nmol/L after 1 mg dexamethasone administered overnight suggests hypercortisolism. False positive responses – non-compliance, malabsorption, drugs inducing the hepatic metabolism of dexamethasone (phenytoin, carbamazepine, phenobarbital, rifampicin), drugs elevating CBG (oestrogens), chronic kidney disease, acute illness and pseudo-Cushing’s (depression, alcohol abuse, eating disorders). False negative responses – nephrotic syndrome (↓CBG), renal dialysis, chronic liver disease (reduced metabolism and clearance of dexamethasone). Sensitivity 98-100%, Specificity 85% NOTES: 25% of hospitalised inpatients will have an abnormal 1 mg dexamethasone suppression test, if possible, investigations should be delayed until acute illness has subsided. 2.2 LATE NIGHT SALIVARY CORTISOL PREPARATION & PROCEDURE: Patient to collect Salivettes from clinic or laboratory collection centre. Patient should chew on Salivette for 2 minutes (or until saturated with saliva) between 11pm to midnight prior to brushing their teeth, and not within 30 mins of eating or drinking. Minimum of two separate samples should be collected. Salivary cortisol is stable at room temperature. Patient should drop or post Salivettes back to laboratory collection centre. Smokers should avoid cigarette smoking on the day of the test. Time Procedure Comment 11pm Chew on salivette provided for minutes until saturated. Collect prior to brushing teeth and nil by mouth for at least 30 mins prior to collection. INTERPRETATION: Normal response – Consult reference intervals provided by the laboratory. False positive responses – smokers and especially patients who chew tobacco, contamination of salivettes with corticosteroid, bleeding of the gum, shift workers. False negative responses - non-compliance with collection procedure (drinking water dilutes the sample), cyclical Cushing’s.