Table 2. Caveats and Restrictions for Tests Used to Screen for Hypercortisolism.

Test	Caveat	When can the test be used despite the caveat?	Verifying the result
All tests	May be falsely normal in a patient with cyclic Cushing's syndrome [10,11]	If the pre-test probability is high based on history and physical examination, repeat testing at intervals or when patient feels worst.	Review caveats for each test below
UFC	May be falsely increased with fluid intake >5 L/day [12]	If subjects reduce intake	Measure volume; if volume is high, ask about intake
	May be falsely increased or decreased with incorrect collection		Measure creatinine, which should be ± 15% from day to day; check volume
	Will be decreased in the setting of renal impairment [13]	Use with caution with GFR 30–50 mL/min: accept as valid only elevated values.
1 mg DST	May be falsely normal in Cushing's disease patients, presumably because of slow drug metabolism [14]		Measure dexamethasone; if in range expected of an 8 mg dose, consider Cushing's disease
	May be falsely abnormal in patients with elevated CBG (2° oral estrogen) or in those with fast metabolism of dexamethasone [8]	Fewest false positive results in patients not taking medications that interact with CYP3A4 [15]	Measure dexamethasone level; if low, increase dose to achieve correct level
			Measure CBG; if high discontinue estrogen for 4–6 weeks
Salivary cortisol	May be falsely abnormal in older men and women, and in hypertensive or diabetic patients [16,17]	If used in these populations, consider accepting only normal results
	May be falsely abnormal in individuals with variable sleeping times (e.g., shift workers)	If used in this population, consider accepting only normal results

UFC, urine free cortisol; GFR, glomerular filtration rate; 1 mg DST, 1 mg overnight dexamethasone suppression test; CBG, corticosteroid-binding globulin.