The most appropriate diagnostic test to perform next is the low-dose dexamethasone suppression test to screen for the autonomous secretion of cortisol. The increasing use of imaging studies for various medical indications has revealed otherwise unrecognized adrenal masses in less than 1% of the population younger than 30 years and up to 7% of those older than 70 years. Ten to 15% of adrenal incidentalomas are functional, although most have no overt clinical manifestations. Therefore, testing is usually necessary to identify functional tumors secreting catecholamines, cortisol, or aldosterone. Of the functional adenomas, most secrete excessive amounts of cortisol. In subclinical Cushing syndrome (CS), classic signs or symptoms of cortisol excess are not observed; however, complications of long-standing hypercortisolism may result. The patient has two disorders that can be seen in association with subclinical CS: type 2 diabetes mellitus and osteoporosis. Obesity and hypertension are also common. The low-dose overnight dexamethasone suppression test is recommended as the initial screening test for this condition due to its high sensitivity. Screening for pheochromocytoma, such as by measuring 24-hour urine fractionated metanephrines and catecholamines, is also indicated in all patients with an incidentally noted adrenal mass.

Adrenal vein sampling (AVS) is not needed. AVS is most often performed to evaluate for a bilateral versus unilateral adrenal cause of primary hyperaldosteronism.

Measurement of plasma renin activity and aldosterone concentration is not indicated in patients without hypertension.

No further testing is also inappropriate. Although the imaging characteristics of the mass are in keeping with a benign adrenal adenoma, further diagnostic evaluation is needed. This includes testing for autonomous hormonal secretion and subsequent radiographic surveillance (first at 3-6 months and then annually for 1-2 years).