A 48-year-old woman with newly diagnosed hypertension has serum potassium of 2.9 mEq/L on routine testing. She is not on diuretics. ECG shows U waves. Which investigation is most appropriate as the next step in evaluation?

• A Plasma renin activity alone
• B Renal Doppler ultrasound
• C 24-hour urinary cortisol
• D Plasma aldosterone concentration and plasma renin activity to calculate aldosterone-to-renin ratio ✓

Explanation

Hypertension with spontaneous hypokalemia in the absence of diuretic use should raise suspicion for primary hyperaldosteronism. The aldosterone-to-renin ratio is the recommended screening test. An aldosterone level above 15 ng/dL with a suppressed renin and a ratio above 20 to 30 is suggestive. Renal Doppler evaluates for renal artery stenosis, which causes renin-mediated hypertension but typically does not produce unprovoked hypokalemia to this degree. Urinary cortisol screens for Cushing syndrome, which also causes hypertension and hypokalemia but is less common.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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