Final answer:
With a phenytoin blood level of 35 mcg/mL, symptoms of phenytoin toxicity such as ataxia would be expected; therefore, the correct answer is B. Ataxia.
Step-by-step explanation:
A client with epilepsy who is on phenytoin therapy with a blood level of 35 mcg/mL is presenting with a level above the usually recommended therapeutic range of 10-20 mcg/mL. At this elevated level, the client is at risk for phenytoin toxicity. Symptoms of phenytoin toxicity may include ataxia which is a lack of muscle coordination affecting gait and movement, slurred speech, nausea and vomiting, and even increased seizures due to neuronal overexcitability from toxic levels of the medication.
Answering the question directly based on the provided lab result and typical symptoms of phenytoin toxicity, the symptom that would be expected as a result of this laboratory result is B. Ataxia.