Examkin

Question

Difficulty: MediumOrdering Laboratory Tests

A 3838-year-old woman is evaluated in the clinic for episodes of severe palpitations, pounding headaches, and profuse sweating. These episodes occur unexpectedly, last for 1515 to 2020 minutes, and resolve spontaneously. She has had four such episodes over the past month. During a recent episode, she was evaluated at an urgent care center where her blood pressure was 185/110 mmHg185/110\text{ mmHg} and her heart rate was 115/min115\text{/min}. Today, she feels well. Her blood pressure is 122/78 mmHg122/78\text{ mmHg} and heart rate is 72/min72\text{/min}. The physical examination is unremarkable. Which of the following is the most appropriate next step in laboratory evaluation?

  1. Measurement of plasma free metanephrinesAnswer
  2. B
    Clonidine suppression test
  3. C
    Computed tomography of the abdomen and pelvis
  4. D
    24-hour urinary 5-hydroxyindoleacetic acid excretion
  5. E
    Measurement of plasma aldosterone concentration to plasma renin activity ratio

Answer

The most appropriate next step in laboratory evaluation is the measurement of plasma free metanephrines.
The correct answer identifies the need for highly sensitive biochemical screening as the first step in diagnosing a suspected pheochromocytoma. This patient's episodic severe hypertension, accompanied by the classic triad of headache, sweating, and palpitations, strongly suggests this diagnosis. Measurement of plasma free metanephrines is highly sensitive and is the preferred initial laboratory evaluation.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient presents with the classic triad of episodic headaches, sweating, and tachycardia (palpitations), accompanied by paroxysmal severe hypertension.
Identifying the classic clinical pattern is essential for formulating an accurate differential diagnosis.
2
Formulate the most likely diagnosis.
The clinical picture is highly suspicious for a pheochromocytoma, a catecholamine-secreting tumor of the adrenal medulla.
Pheochromocytomas release catecholamines episodically, leading to the paroxysmal symptoms described.
3
Determine the appropriate diagnostic sequence for the suspected condition.
The initial step is biochemical confirmation of catecholamine excess using a highly sensitive screening test.
Biochemical testing must precede imaging to confirm the diagnosis and prevent the discovery of incidental, non-functioning adrenal masses.
4
Select the best initial laboratory test.
Measurement of plasma free metanephrines or 24-hour urine fractionated metanephrines is the test of choice.
These tests have the highest sensitivity for detecting a pheochromocytoma.

Key Concept

The initial evaluation of a suspected pheochromocytoma requires biochemical confirmation of catecholamine excess, most commonly through the measurement of plasma free metanephrines, prior to any localizing imaging studies.
Estimated Time:1m 15s
Rate this question

Topics

Ordering Laboratory Tests

More questions from this topic