Table 1.

Diagnostic accuracy and limitations of traditional first-line biochemical tests, as well as the newer hair tests used for the diagnosis of Cushing’s syndrome (14–18).

Test	Sensitivity	Specificity	Disadvantages
Low-Dose Dexamethasone Suppression Test	>95%	80-85%	• Variation in absorption and metabolism of dexamethasone (e.g., P450 enzyme system interactions, liver or renal disease) between patients may influence results • False positives in women taking oral contraceptive pills and during pregnancy due to increased cortisol binding globulin (CBG) • Poor performance in differentiating from nonneoplastic hypercortisolism • Incompliance may cause a false-positive result • No possibility to test cortisol levels in retrospect as is useful in cyclic CS
Late Night Salivary Cortisol	90-98%	90-100%	• False positives in patients who smoke or use chewing tobacco, and with direct contamination of the saliva with exogenous steroids • Influenced by abnormal sleep-wake cycles • False positives in patients of older age and those with hypertension and diabetes mellitus • False positives in foods that contain glycyrrhizic acid (e.g., licorice, teas) • No possibility to test cortisol levels in retrospect as is useful in cyclic CS
24 Hour Urine Free Cortisol	70-75%	40-90%	• Potential for improper collection • Day-to-day intra-patient variability, often requiring repeated measurements • Possible contamination • Poor performance in differentiating from nonneoplastic hypercortisolism • Measurements influenced by gender, age, urinary volume, sodium intake, and renal function • No possibility to test cortisol levels in retrospect as is useful in cyclic CS
Hair Cortisol	81%	88%	• Limited if no or little scalp hair is present • Method is not yet widely available and, therefore, samples often need mailing to expert laboratories
Hair Cortisone	87%	90%	• Limited if no or little scalp hair is present • Method is not yet widely available and, therefore, samples often need mailing to expert laboratories