A nurse is caring for a client with bacterial pneumonia and has received an order for antibiotics. Which diagnostic test must be ordered before initiating antibiotic therapy to ensure appropriate treatment?

Choice A reason: Sodium 138 mEq/L is normal (135–145 mEq/L), indicating no immediate concern. Abnormal sodium levels risk neurological or cardiac issues, but this value is normal, making it a lower priority compared to an abnormal potassium level, which poses immediate cardiac risks.

Choice B reason: Potassium 3.2 mEq/L indicates hypokalemia (normal 3.5–5.0 mEq/L), risking arrhythmias, muscle weakness, and respiratory compromise. Low potassium disrupts membrane potential, affecting cardiac and skeletal muscle function, making this the priority finding requiring immediate correction to prevent life-threatening complications.

Choice C reason: Glucose 110 mg/dL is within normal fasting range (70–110 mg/dL), indicating no urgent concern. Abnormal glucose levels risk metabolic issues, but this value is normal, making it a lower priority compared to hypokalemia, which poses immediate cardiac risks in this client.

Choice D reason: Hemoglobin 12 g/dL is borderline low (normal 13–17 g/dL males, 12–15 g/dL females) but not immediately life-threatening. Anemia may cause fatigue, but hypokalemia’s cardiac risks are more urgent, making hemoglobin a secondary priority in this laboratory review.

Choice A reason: A basic metabolic panel assesses electrolytes and renal function but does not identify the bacterial cause of pneumonia. It supports overall patient status but does not guide antibiotic selection, making it less critical than sputum culture for ensuring targeted, effective antibiotic therapy.

Choice B reason: Sputum culture and sensitivity identify the specific bacteria causing pneumonia and their antibiotic susceptibilities, ensuring targeted therapy. Inappropriate antibiotics risk treatment failure and resistance. Obtaining the culture before antibiotics prevents false-negative results, making this critical for effective treatment.

Choice C reason: A chest radiograph confirms pneumonia’s presence and extent but does not identify the causative organism or antibiotic sensitivity. It supports diagnosis but does not guide specific antibiotic therapy, making it less critical than sputum culture for ensuring appropriate treatment.

Choice D reason: A complete blood count with differential shows infection severity (e.g., elevated white cells) but does not identify specific bacteria or antibiotic sensitivity. It supports diagnosis but is secondary to sputum culture, which ensures targeted antibiotic selection for effective pneumonia treatment.