An established patient in the primary care clinic, a 47-year-old male, is evaluated during a follow-up visit for difficult-to-control blood pressure. He reports taking his prescribed regimen of maximum-dose lisinopril, amlodipine, and chlorthalidone consistently. He occasionally experiences mild muscle cramps in his calves but otherwise feels well. Blood pressure is 164/96 mmHg and heart rate is 76/min. Physical examination is unremarkable with no abdominal bruits, edema, or focal neurological deficits. A basic metabolic panel reveals a serum sodium of 144 mEq/L, a serum potassium of 3.1 mEq/L, and a serum creatinine of 0.9 mg/dL. Which of the following is the most appropriate next step in the laboratory evaluation of this patient?
- Measurement of morning plasma aldosterone concentration and plasma renin activityAnswer
- BOral sodium loading test followed by measurement of 24-hour urine aldosterone
- CComputed tomography (CT) scan of the adrenal glands without intravenous contrast
- DDiscontinuation of chlorthalidone and repeat basic metabolic panel in one month
- EImmediate hospital admission for continuous electrocardiographic monitoring and intravenous potassium
Answer
Measurement of morning plasma aldosterone concentration and plasma renin activity
The correct sequence for diagnosing primary aldosteronism begins with biochemical screening. The patient presents with resistant hypertension (blood pressure above target despite concurrent use of three antihypertensive agents of different classes, one of which is a thiazide-like diuretic) and hypokalemia. This triad is highly suspicious for primary aldosteronism (Conn syndrome). The most appropriate initial laboratory evaluation is measuring the morning plasma aldosterone concentration (PAC) and plasma renin activity (PRA). A PAC/PRA ratio greater than 20 with a PAC greater than 15 ng/dL strongly suggests the diagnosis and justifies moving to confirmatory testing.
Step-by-Step Solution
Key Concept
Patients presenting with resistant hypertension and hypokalemia (whether spontaneous or diuretic-induced) should be screened for primary aldosteronism using the plasma aldosterone concentration to plasma renin activity ratio.