Table 2.
Test | Basis of Test | Methodology | Convenience | Sensitivity and Specificity (%)[11] | Cautions |
---|---|---|---|---|---|
LNSC | Measures the disruption in the normal circadian rhythm seen with hypercortisolism | Salivary sample is collected between 2300 h and 2400 h; test should be repeated. | ✓✓✓✓ | Sensitivity: 92-100 Specificity: 93-100 | •Not taking the sample late at night significantly affects results. |
•Cortisol levels can be abnormally high in those with altered sleep patterns (e.g., shift workers) and in those who smoke. | |||||
•Lower sensitivity for less severe hypercortisolism | |||||
24-h UFC | Measures UFC over the course of a day | All urine is collected over a 24-h period, discarding the first void. | ✓ | Sensitivity: 80-98 Specificity: 45-98 | •Lower specificity and sensitivity compared with other methods for less severe hypercortisolism |
•High fluid intake, contamination, incomplete urine collection, certain drugs, and decreased glomerular filtration rate (<60 mL/min) may affect accuracy. | |||||
ODST (using 1.8 µg/dL cutoff) | Measures the amount of suppression by dexamethasone of ACTH and thereby, cortisol secretion; suppression is not observed in those with hypercortisolism | Oral dexamethasone (1 mg) is administered between 2300 h and 2400 h, and serum cortisol is collected between 0800 h and 0900 h the next morning. | ✓✓✓ | Sensitivity: 85-90 Specificity: 95-99 | •The fixed doses used in the tests do not take into consideration differences in dexamethasone absorption, volume of distribution, and metabolism, all of which are influenced by gastrointestinal function, body weight/composition, and hepatic and renal function. |
•Falsely assumes all corticotroph adenomas have decreased sensitivity to dexamethasone, all ectopic ACTH-secreting tumors are insensitive to dexamethasone, and cortisol-secreting adenomas cannot be inhibited by dexamethasone | |||||
LDDST | Measures the amount of suppression by dexamethasone of ACTH, and thereby, cortisol secretion; suppression is not observed in those with hypercortisolism | Oral dexamethasone (0.5 mg) is administered beginning at 0900 h on day 1 with repeated administration at 6-h intervals for 48 h (1500, 2100, 0300 h); serum cortisol is collected 6 h after the last dose (0900 h). | ✓✓ | Sensitivity: 91-98 | •The fixed doses used in the tests do not take into consideration differences in dexamethasone absorption, volume of distribution, and metabolism, all of which are influenced by gastrointestinal function, body weight/composition, and hepatic and renal function. |
Specificity: 70-95 | •Falsely assumes all corticotroph adenomas have decreased sensitivity to dexamethasone, all ectopic ACTH-secreting tumors are insensitive to dexamethasone, and cortisol-secreting adenomas cannot be inhibited by dexamethasone |
Abbreviations: ✓, indicates lowest convenience; ✓✓✓✓, indicate highest convenience; LDDST, low-dose DST; ODST, overnight DST.