Which of the following is a sign of infiltration at an IV site?

Swelling and discomfort at the IV site are key indicators of infiltration, a condition where IV fluid inadvertently enters the surrounding tissue rather than the intended vein. As the fluid collects outside the vein, it causes the area to become swollen, often resulting in discomfort or a sense of tightness. This is typically accompanied by a decrease in the effectiveness of the IV therapy, as the fluid is not being delivered into the bloodstream where it's needed.

The other signs mentioned in other options do not specifically indicate infiltration. For example, redness and increased warmth often suggest phlebitis or infection rather than infiltration. Pain upon medication administration can occur for a variety of reasons, including irritation from the medication itself or other complications unrelated to infiltration. Fluid retention in the limb may occur due to underlying health issues or other types of complications but is not a definitive sign of infiltration either.