Final answer:
The therapeutic serum drug level for phenytoin, used for seizure control, is between 10 and 20 mcg/mL. Thus, a level of 15 mcg/mL indicates a therapeutic serum drug result.
Step-by-step explanation:
The client is taking phenytoin for seizure control, and a blood sample for a serum drug level is drawn. Which laboratory finding indicates a therapeutic serum drug result? The therapeutic range of phenytoin in the blood is generally considered to be between 10 and 20 mcg/mL. Therefore, the correct answer to the question is B. 15 mcg/mL, which falls within the therapeutic range and indicates a proper serum level for seizure control. Values below this range may not be effective, and values above could indicate potential drug toxicity. It's critical to monitor these levels to both avoid drug toxicity and to reduce therapeutic costs.