A 40-year-old woman presents to the clinic for follow-up of hypertension which has been difficult to control despite several anti-hypertensive medications. Her blood pressure is consistently measured between 160/100 and 180/110 mm Hg during multiple visits over the past several months. She reports feeling fatigued and has noticed muscle weakness over the past few months. Past medical history is negative other than the hypertension. She currently takes amlodipine and hydralazine. She had side effects from hydrochlorothiazide and lisinopril, so these medications were previously discontinued. Laboratory results reveal the following:
A CT scan of the abdomen shows a 2.5-cm mass in the right adrenal gland. Which of the following additional findings would be expected in this patient?
C) Low plasma renin activity, high serum aldosterone, high serum bicarbonate
This patient's presentation of hypertension, hypokalemia, and a unilateral adrenal mass is highly suggestive of primary hyperaldosteronism (Conn syndrome). Primary hyperaldosteronism is characterized by the excessive and unregulated secretion of aldosterone from the adrenal glands, commonly due to an adrenal adenoma or bilateral adrenal hyperplasia.
Aldosterone increases renal reabsorption of sodium, which leads to an increase in total body sodium. Despite this, serum sodium is usually normal or mildly elevated because of a compensatory increase in antidiuretic hormone (ADH) since the hypothalamic-pituitary-adrenal (HPA) axis is intact, and as serum osmolarity increases, so does the release of ADH. This is why a normal serum sodium is seen in a Conn syndrome. The elevated levels of aldosterone results in the suppression of renin release from the kidneys, resulting in low plasma renin activity (PRA). Aldosterone also promotes potassium excretion, leading to hypokalemia, which can cause muscle weakness and fatigue. Furthermore, aldosterone stimulates hydrogen ion secretion, resulting in metabolic alkalosis, reflected by elevated serum bicarbonate levels.
Answer choice A: High plasma renin activity, high serum aldosterone, high serum bicarbonate, is incorrect. Elevated renin activity would be inconsistent with primary hyperaldosteronism.
Answer choice B: High plasma renin activity, high serum aldosterone, low serum bicarbonate, is incorrect. This pattern would be more consistent with secondary hyperaldosteronism, where renin activity is elevated due to conditions such as renovascular hypertension.
Answer choice D: Low plasma renin activity, high serum aldosterone, low serum bicarbonate, is incorrect. Low serum bicarbonate would suggest an acidosis rather than the metabolic alkalosis that is expected in primary hyperaldosteronism.
Answer choice E: Low plasma renin activity, low serum aldosterone, high serum bicarbonate, is incorrect. Low serum aldosterone would not fit with the clinical scenario of primary hyperaldosteronism.
Key Learning Point
Primary hyperaldosteronism is characterized by resistant hypertension, hypokalemia, and possibly an adrenal mass, low plasma renin activity, high serum aldosterone, and high serum bicarbonate due to metabolic alkalosis.
