Incidentaloma laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Overview

Laboratory findings consistent with the diagnosis of incidentaloma include an abnormal 1 mg overnight dexamethasone for subclinical Cushing's syndrome that should be confirmed with 24-hour urinary free cortisol, serum ACTH concentration, and dehydroepiandrosterone sulfate (DHEAS). In patients with adrenal masses that have a probability for pheochromocytoma, routine measurement of 24-hour urinary fractionated metanephrines and catecholamines should be done. All patients with hypertension and an adrenal incidentaloma should be evaluated by measurements of plasma aldosterone concentration and plasma renin activity.

Laboratory Findings

Subclinical Cushing's syndrome

• Subclinical Cushing's syndrome should be ruled out by performing the 1 mg overnight dexamethasone suppression test (DST).
• An abnormal 1 mg overnight dexamethasone should be confirmed with 24-hour urinary free cortisol, serum ACTH concentration, and dehydroepiandrosterone sulfate (DHEAS).

• An undetectable level of serum ACTH is also supportive of the diagnosis of subclinical Cushing’s syndrome.

• Hormonal evaluation in the patients with subclinical Cushing's syndrome showed the following: [11]:

• Low baseline secretion of ACTH
• Lack of suppressibility of cortisol secretion after 1 mg dexamethasone
• Supranormal 24-hour urinary cortisol excretion
• Disturbed cortisol circadian rhythm
• Blunted plasma ACTH responses to corticotropin-releasing hormone (CRH)

Pheochromocytoma

• In patients with adrenal masses that have a probability for pheochromocytoma, routine measurement of 24-hour urinary fractionated metanephrines and catecholamines should be done.

Aldosteronomas

• All patients with hypertension and an adrenal incidentaloma should be evaluated by measurements of plasma aldosterone concentration and plasma renin activity.
• measurement of plasma aldosterone to renin ratio (ARR) is the best initial test for the evaluation of primary aldosteronism (44, 106, 111). A range of ARR cutoff values from 20 to 100
• A serum aldosterone level below 0.25 nmol/liter (9 ng/dl) makes a diagnosis of primary aldosteronism highly unlikely (113, 114).

• Borderline values should be repeated:

1. After correcting hypokalemia
2. While the patient is on salt restriction
3. In the morning in a sitting position
4. After resting for at least 15 min before proceeding with confirmatory tests (44, 91)

• Patients with an elevated ARR should proceed with a confirmatory test such as the salt loading test or saline suppression test (44, 115).