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Difficulty: MediumDiagnostic Workup and Test Sequencing

A 34-year-old man comes to the clinic for a follow-up examination of poorly controlled hypertension. He was diagnosed with hypertension two years ago and is currently taking amlodipine, lisinopril, and hydrochlorothiazide at maximally tolerated doses. He reports no headaches, chest pain, palpitations, or abnormal sweating. His blood pressure is 162/100162/100 mm Hg, and his pulse is 7878/min. His BMI is 2424 kg/m 2^2. Physical examination shows no abdominal bruits, delayed femoral pulses, or cushingoid features. Laboratory studies reveal:

Sodium: 142142 mEq/L
Potassium: 2.92.9 mEq/L
Chloride: 104104 mEq/L
Bicarbonate: 2828 mEq/L
Creatinine: 0.90.9 mg/dL

Which of the following is the most appropriate next step in the diagnostic workup of this patient?

  1. Measurement of plasma aldosterone concentration and plasma renin activityAnswer
  2. B
    Adrenal venous sampling
  3. C
    Oral sodium loading test
  4. D
    Noncontrast CT scan of the abdomen
  5. E
    Renal duplex ultrasonography

Answer

Measurement of plasma aldosterone concentration and plasma renin activity
The correct answer is measurement of plasma aldosterone concentration and plasma renin activity. This patient presents with resistant hypertension (blood pressure >140/90>140/90 mm Hg despite adherence to three antihypertensive medications of different classes, including a diuretic) and significant spontaneous hypokalemia. This clinical picture is highly suspicious for primary hyperaldosteronism. The diagnostic algorithm for primary hyperaldosteronism follows a strict sequential framework: initial screening, biochemical confirmation, and finally, subtype classification (localization). The most appropriate initial screening test is the early morning plasma aldosterone concentration (PAC) to plasma renin activity (PRA) ratio (ARR). A high ARR (typically >20>20) with a PAC >15>15 ng/dL suggests the diagnosis and prompts confirmatory testing.

Step-by-Step Solution

1
Identify the clinical syndrome from the patient's presentation.
The patient has resistant hypertension (uncontrolled on three medications including a diuretic) accompanied by spontaneous hypokalemia and metabolic alkalosis.
Recognizing this triad strongly suggests a diagnosis of primary hyperaldosteronism (Conn syndrome).
2
Determine the standard diagnostic sequence for the suspected condition.
The evaluation of primary hyperaldosteronism follows a strict sequence: 1) Screening, 2) Confirmation, and 3) Subtype evaluation/Localization.
Sequential testing minimizes false positives, prevents unnecessary invasive procedures, and ensures cost-effective care.
3
Select the appropriate initial screening test.
The aldosterone-to-renin ratio (ARR), obtained by measuring plasma aldosterone concentration (PAC) and plasma renin activity (PRA), is the indicated next step.
It is a highly sensitive, non-invasive first-line test for primary hyperaldosteronism.

Key Concept

The diagnostic workup for primary hyperaldosteronism requires step-wise progression starting with an aldosterone-to-renin ratio (ARR) screening, followed by confirmatory testing (e.g., oral sodium loading), and finally localization (e.g., CT scan and adrenal venous sampling).
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Diagnostic Workup and Test Sequencing

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