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Difficulty: HardOrdering Laboratory Tests

A 58-year-old man comes to the clinic for follow-up of a recently discovered adrenal mass. Two weeks ago, he presented to the emergency department with left lower quadrant abdominal pain and was diagnosed with uncomplicated diverticulitis via a noncontrast abdominal computed tomography (CT) scan. The CT scan incidentally revealed a 3.2-cm right adrenal nodule. A subsequent dedicated adrenal-protocol CT scan characterizes the mass as a benign-appearing adenoma. The patient's diverticulitis has completely resolved following a course of oral antibiotics. He feels well and reports no headaches, palpitations, or unexplained weight changes. Medical history is unremarkable, and he takes no medications. Blood pressure is 118/76 mmHg, pulse is 72/min, and BMI is 24 kg/m². Physical examination reveals no abdominal striae, supraclavicular fat pads, or proximal muscle weakness. Which of the following is the most appropriate next step in laboratory evaluation?

  1. A
    24-hour urine collection for cortisol, aldosterone, and fractionated metanephrines
  2. 1-mg overnight dexamethasone suppression test and plasma fractionated metanephrinesAnswer
  3. C
    1-mg overnight dexamethasone suppression test, plasma fractionated metanephrines, and plasma aldosterone-to-renin ratio
  4. D
    Early morning serum cortisol and adrenocorticotropic hormone (ACTH) levels
  5. E
    No further laboratory evaluation is indicated due to the benign imaging characteristics

Answer

1-mg overnight dexamethasone suppression test and plasma fractionated metanephrines
All adrenal incidentalomas, regardless of benign imaging characteristics, must be biochemically evaluated to rule out functional hormone secretion. The standard initial laboratory evaluation includes screening for autonomous cortisol secretion using a 1-mg overnight dexamethasone suppression test, and screening for pheochromocytoma using plasma fractionated metanephrines (or 24-hour urinary fractionated metanephrines). While screening for primary aldosteronism using a plasma aldosterone-to-renin ratio is also part of the adrenal incidentaloma algorithm, it is exclusively indicated for patients who have concurrent hypertension or unexplained hypokalemia. Because this patient is normotensive, asymptomatic, and not on any medications, testing for primary aldosteronism is unnecessary.

Step-by-Step Solution

1
Analyze the clinical presentation and imaging findings.
The patient has an incidentally discovered 3.2-cm adrenal mass that appears benign on imaging. He is asymptomatic, normotensive, and has no clinical signs of endocrine syndromes.
Identifying the clinical status and imaging characteristics determines the necessity and scope of the biochemical workup.
2
Determine the standard biochemical workup for an adrenal incidentaloma.
Guidelines recommend screening all adrenal incidentalomas for subclinical autonomous cortisol secretion and pheochromocytoma.
Even benign-appearing adenomas can secrete hormones and cause subclinical disease with long-term cardiovascular morbidity.
3
Evaluate the need for primary aldosteronism screening.
The patient is normotensive without hypokalemia; therefore, screening with a plasma aldosterone-to-renin ratio is not indicated.
Aldosteronism screening is reserved only for patients who present with hypertension or unexplained hypokalemia.
4
Select the appropriate laboratory tests based on the determined requirements.
A 1-mg overnight dexamethasone suppression test (for cortisol) and plasma fractionated metanephrines (for pheochromocytoma) are the most appropriate next tests.
These are the highly sensitive, first-line screening tests recommended by endocrine society guidelines for normotensive patients.

Key Concept

All adrenal incidentalomas require biochemical screening for autonomous cortisol secretion (using a 1-mg overnight dexamethasone suppression test) and pheochromocytoma (using plasma or urinary fractionated metanephrines). Screening for primary aldosteronism is only added if the patient has hypertension or unexplained hypokalemia.
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Ordering Laboratory Tests

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