**Core Concept**
Primary hyperaldosteronism is a condition characterized by the excessive production of aldosterone, a hormone produced by the adrenal glands that regulates electrolyte balance and blood pressure. This excess aldosterone leads to sodium retention, potassium excretion, and water retention, ultimately resulting in hypertension and hypokalemia.

**Why the Correct Answer is Right**
Hyperaldosteronism is characterized by the excessive excretion of potassium ions (K+) in the urine, leading to hypokalemia (low potassium levels in the blood). This occurs due to the stimulation of sodium-potassium exchange in the collecting ducts of the kidneys. As a result, patients with primary hyperaldosteronism typically present with hypokalemia, which can manifest as muscle weakness, fatigue, and cardiac arrhythmias. The correct answer, hyperkalemia (elevated potassium levels in the blood), is not a feature of primary hyperaldosteronism.

**Why Each Wrong Option is Incorrect**
**Option A:** Polyuria is not a direct feature of primary hyperaldosteronism, but rather a consequence of the associated hypokalemia and its effects on renal function. However, in the context of primary hyperaldosteronism, patients may experience polyuria due to the effects of hypokalemia on the renal collecting ducts.
**Option B:** Hypertension is a hallmark feature of primary hyperaldosteronism, resulting from the excessive sodium retention and water retention caused by excess aldosterone.
**Option C:** Hypokalemia is a characteristic feature of primary hyperaldosteronism, as explained above.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that primary hyperaldosteronism can be caused by either a unilateral aldosterone-producing adenoma or bilateral adrenal hyperplasia. The Conn's syndrome, a classic presentation of primary hyperaldosteronism, typically includes hypertension, hypokalemia, and suppressed plasma renin activity.

✓ Correct Answer: D. Hyperkalemia