The nurse notices which lab finding indicating the effect of fludrocortisone?

Fludrocortisone is a synthetic corticosteroid that mimics the effects of aldosterone, a hormone that plays a crucial role in regulating electrolyte and fluid balance in the body. One of its primary effects is to promote sodium retention and potassium excretion by the kidneys.

When fludrocortisone is administered, it leads to a decrease in serum potassium levels due to its mineralocorticoid activity. This occurs as the drug promotes the reabsorption of sodium in exchange for potassium, causing potassium to be excreted in greater amounts. Consequently, the lower serum potassium level is a direct indicator of the drug's pharmacological effects.

Although increased serum sodium levels may also be a result of fludrocortisone use, the specific decrease in serum potassium is a more direct and notable laboratory change associated with the drug's action, making it the more appropriate answer in this context. Other options, such as elevated red blood cell count or increased serum calcium, are not directly influenced by fludrocortisone and thus do not reflect its specific effects in the body.