What laboratory finding places a client at risk while receiving digoxin?

Hypokalemia significantly increases the risk for toxicity in clients receiving digoxin. Digoxin works by inhibiting the sodium-potassium ATPase pump, which can increase the intracellular calcium concentration, ultimately enhancing cardiac contractility. However, potassium is essential for maintaining normal cardiac function and stabilizing myocardial cells. When potassium levels are low, as seen in hypokalemia, there is an increased propensity for digoxin to bind to these sites, leading to a greater effect of digoxin, which can result in toxicity.

In a scenario of hypokalemia, heart arrhythmias, which are one of the primary concerns with digoxin therapy, become more likely. Thus, monitoring potassium levels and ensuring they remain within an acceptable range is crucial for clients on digoxin to prevent adverse effects and ensure efficacy in managing heart failure or other cardiac issues.

The other choices do not have the same direct relationship to the safety of digoxin therapy. While conditions like hyponatremia or hypercalcemia may have implications for overall health or could affect heart function, they do not specifically increase the risk of digoxin toxicity in the way that low potassium levels do.