A 38-year-old woman is seen in follow-up to discuss the findings of an abdominal and pelvic CT scan done to evaluate renal colic, which has since resolved. The abdominal CT scan showed two small nonobstructing renal calculi in the right kidney and a 1.6-cm left adrenal mass with a density of 21 Hounsfield units (indeterminate for adrenal adenoma). Other than nephrolithiasis, the remainder of the medical history is unremarkable, and she takes no medications.
On physical examination, vital signs and the remainder of the examination are unremarkable.
Laboratory studies show normal serum electrolytes.
Which of the following is the most appropriate test to perform next?
A. 24-Hour urine free cortisol measurement
B. 24-Hour urine total metanephrine measurement
C. Plasma aldosterone-plasma renin ratio (ARR) measurement
D. Serum dehydroepiandrosterone sulfate (DHEAS) measurement
MKSAP Answer and Critique
The correct answer is B. 24-Hour urine total metanephrine measurement. This content is available to MKSAP 18 subscribers as Question 39 in the Endocrinology and Metabolism section. More information about MKSAP is available online.
The most appropriate next test to perform is a 24-hour urine total metanephrine measurement to screen for pheochromocytoma. Even though this patient does not have hypertension, she should be screened for pheochromocytoma, as these tumors may exist in the absence of typical symptoms or hypertension. Approximately 50% of pheochromocytomas are now first discovered as an incidental adrenal mass. An alternative screening test for pheochromocytoma is measuring the fractionated free plasma metanephrine level. This test has a false-positive rate of approximately 11%, and, therefore, may be considered more useful when suspicion for pheochromocytoma is high. This patient should also be screened for subclinical Cushing syndrome with a 1-mg overnight dexamethasone suppression test. The prevalence of incidentally noted adrenal masses increases with age and is estimated to be about 10% in the elderly. Most lesions are benign, nonfunctioning adenomas, and approximately 10% to 15% secrete excess hormones.
The 24-hour urine free cortisol test is not sensitive enough to diagnose subclinical autonomous cortisol secretion from an adrenal mass. The 24-hour urine free cortisol levels are usually within the normal range in subclinical Cushing syndrome.
The patient does not require screening for primary aldosteronism with a plasma aldosterone-plasma renin ratio (ARR) as she does not have hypertension. Only patients with an incidental adrenal mass and hypertension require screening for primary aldosteronism. Hypokalemia, traditionally thought to be a key feature of primary aldosteronism, is no longer a prerequisite for diagnosis because many patients with this disorder have normal potassium levels.
In women, rapid onset of hirsutism, menstrual irregularities, and virilization should raise suspicion for tumoral hyperandrogenism. Measurement of dehydroepiandrosterone sulfate (DHEAS) is not indicated in this patient, as she did not show signs of hyperandrogenism (hirsutism, deep voice, male pattern balding, clitoromegaly). Serum DHEAS may be measured if signs of significant hyperandrogenism are present in the setting of an adrenal mass that has radiologic features suspicious for malignancy (size >4 cm, heterogeneous enhancement with contrast administration, irregular margins, presence of calcifications or necrosis).
- Biochemical testing for pheochromocytoma should be undertaken in all patients with an adrenal mass, even in the absence of typical symptoms or hypertension.