What is the hallmark laboratory finding in primary hyperaldosteronism?

In primary hyperaldosteronism, also known as Conn's syndrome, the hallmark laboratory finding is hypokalemia. This occurs due to the excessive production of aldosterone, which leads to increased reabsorption of sodium in the distal nephron and promotes the secretion of potassium in the urine. As sodium levels increase and are reabsorbed, potassium is lost in higher amounts, resulting in low potassium levels (hypokalemia) in the blood.

Additionally, because aldosterone promotes sodium retention, patients may sometimes present with mild hypernatremia, but it is the hypokalemia that is most characteristic of this condition. The effects of excessive aldosterone are often evident in the laboratory results, making hypokalemia a significant and telling finding in diagnosing primary hyperaldosteronism. This can lead to clinical manifestations such as muscle weakness, fatigue, and hypertension, further supporting the diagnosis when viewed alongside laboratory data.