A nurse is reviewing laboratory values for a client who has bipolar disorder and a prescription for lithium. The nurse should identify that which of the following laboratory results places the client at risk for lithium toxicity?

Choice A reason: Hyponatremia (sodium 130 mEq/L) significantly increases the risk of lithium toxicity. Lithium and sodium compete for reabsorption in the renal tubules. When sodium levels are low, the kidneys retain more lithium, leading to elevated serum levels and potential toxicity. Maintaining normal sodium levels is critical for safe lithium therapy. Choice B reason: A slightly low calcium level does not directly affect lithium metabolism or toxicity risk. While calcium imbalances may have neurological effects, they are not a primary concern in lithium management. Choice C reason: A chloride level of 108 mEq/L is slightly above normal but does not influence lithium pharmacokinetics or toxicity risk. Chloride is not a key factor in lithium excretion or retention. Choice D reason: A potassium level of 5.2 mEq/L is mildly elevated but not directly related to lithium toxicity. Potassium disturbances may occur in various conditions but do not significantly alter lithium clearance.