A 38-year-old man comes to the clinic for a follow-up appointment after a routine pre-employment physical revealed elevated blood pressure. He reports generalized muscle weakness and occasional muscle cramps over the past few months but otherwise feels well. He does not take any medications. His family history is unremarkable. Blood pressure is mm Hg, and pulse is /min. The remainder of the physical examination is unremarkable. An initial basic metabolic panel shows:
| Laboratory Test | Result | Reference Range |
|---|---|---|
| Sodium | mEq/L | - mEq/L |
| Potassium | mEq/L | - mEq/L |
| Chloride | mEq/L | - mEq/L |
| Bicarbonate | mEq/L | - mEq/L |
| Blood urea nitrogen | mg/dL | - mg/dL |
| Creatinine | mg/dL | - mg/dL |
Which of the following is the most appropriate next step in laboratory evaluation?
- Plasma aldosterone concentration and plasma renin activityAnswer
- BIntravenous saline infusion test
- CAdrenal vein sampling
- DMeasurement of 24-hour urine fractionated metanephrines
- ELate-night salivary cortisol measurement
Answer
Plasma aldosterone concentration and plasma renin activity
The correct answer identifies the most appropriate initial screening test for primary hyperaldosteronism. This patient's presentation of significant hypertension, hypokalemia, and metabolic alkalosis in the absence of diuretic use is highly suspicious for autonomous aldosterone secretion. Primary hyperaldosteronism is initially screened by calculating the ratio of plasma aldosterone concentration (PAC) to plasma renin activity (PRA). An elevated PAC/PRA ratio (typically , with PAC ng/dL) is considered a positive screen.
Step-by-Step Solution
Key Concept
The initial screening for suspected primary hyperaldosteronism (suggested by hypertension, hypokalemia, and metabolic alkalosis) involves measuring the plasma aldosterone concentration (PAC) and plasma renin activity (PRA).