What laboratory abnormality is typically associated with Cushing's syndrome?

In Cushing's syndrome, the laboratory abnormality most often observed is hypokalemia. This condition is characterized by excess production of cortisol, which can lead to alterations in electrolyte balance. Cortisol has mineralocorticoid effects, meaning it can promote sodium retention and potassium excretion in the kidneys. As a result, patients with Cushing's syndrome frequently exhibit low levels of potassium in their blood.

The increased sodium retention can also contribute to elevated blood pressure, although this is not the primary electrolyte disturbance associated with Cushing's. Hypokalemia can result in symptoms such as muscle weakness, fatigue, and arrhythmias.

In contrast, conditions like hyperkalemia would suggest a different underlying issue, such as adrenal insufficiency or kidney dysfunction. Hyponatremia and hypernatremia are not specific indicators of Cushing's syndrome; in fact, they are often linked to other endocrine disorders or body fluid distribution issues. Therefore, hypokalemia is a definitive and characteristic laboratory finding associated with Cushing's syndrome.