A previously healthy -year-old man visits a new primary care provider to establish medical care. He reports feeling unusually fatigued over the last few months, accompanied by frequent muscle cramps in his legs and an increase in nighttime urination. He has not seen a physician in five years and currently takes no medications. His blood pressure is mmHg, and his heart rate is /min. Physical examination reveals normal heart sounds, clear lungs, and no abdominal bruits. Laboratory testing shows the following:
| Test | Value |
|---|---|
| Sodium | mEq/L |
| Potassium | mEq/L |
| Chloride | mEq/L |
| Bicarbonate | mEq/L |
| Creatinine | mg/dL |
Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?
- Measurement of plasma aldosterone-to-renin ratioAnswer
- BIntravenous saline infusion test
- CComputed tomography scan of the abdomen
- DAdrenal venous sampling
- ERenal artery duplex ultrasonography
Answer
Measurement of plasma aldosterone-to-renin ratio
The correct answer is measurement of the plasma aldosterone-to-renin ratio. This patient presents with the classic triad of primary hyperaldosteronism: severe hypertension, spontaneous hypokalemia, and metabolic alkalosis. The Endocrine Society guidelines mandate a strict stepwise diagnostic approach. The first step is always biochemical screening using the plasma aldosterone concentration (PAC) to plasma renin activity (PRA) ratio. A high ratio (typically > ) with an elevated PAC (> ng/dL) suggests autonomous aldosterone production (primary hyperaldosteronism), while a low ratio suggests secondary hyperaldosteronism (e.g., renal artery stenosis).
Step-by-Step Solution
Key Concept
The initial step in evaluating suspected primary hyperaldosteronism (suggested by hypertension, hypokalemia, and metabolic alkalosis) is biochemical screening with the plasma aldosterone-to-renin ratio.