What is the most common electrolyte abnormality in patients with Addison's disease?

In patients with Addison's disease, the most common electrolyte abnormality is low sodium, also known as hyponatremia. Addison's disease is characterized by an insufficient production of adrenal hormones, particularly cortisol and aldosterone. Aldosterone plays a critical role in regulating sodium and potassium levels in the body.

When aldosterone levels are low, the kidneys cannot retain sodium effectively, leading to increased sodium loss in urine. This results in a decreased sodium concentration in the bloodstream, causing hyponatremia. Additionally, the lack of cortisol contributes to a relative increase in other hormones, such as antidiuretic hormone (ADH), which can further promote water retention and dilute sodium levels, exacerbating hyponatremia.

In contrast, high potassium levels, or hyperkalemia, can also occur in Addison's disease due to the body's inability to excrete potassium effectively when aldosterone levels are low. However, low sodium is generally the more significant and prevalent abnormality observed in these patients, making it a key feature of Addison's disease. The elevation of potassium and the loss of sodium together contribute to the characteristic biochemical profile of this adrenal insufficiency.