In managing a patient with infective endocarditis, which laboratory test result should the nurse monitor to evaluate the effectiveness of antibiotic therapy?

Choice A rationale A Complete Blood Count (CBC) is used to monitor the white blood cell (WBC) count, which is typically elevated during infection. Normal WBC ranges are 5,000 to 10,000 cells/mm. While a decreasing WBC count can suggest a reduction in the inflammatory response, it is a non-specific indicator of antibiotic success. It does not confirm that the specific causative pathogen of the endocarditis has been eradicated from the bloodstream, making it secondary to more definitive testing. Choice B rationale Blood cultures are the gold standard for evaluating the effectiveness of antibiotic therapy in infective endocarditis. The goal of treatment is to achieve sterile blood, meaning no growth of the infecting organism is detected in subsequent samples. Monitoring for negative blood cultures ensures that the chosen antibiotic and dosage are successfully clearing the bacteremia. This is the most direct way to confirm that the vegetation on the heart valves is no longer shedding bacteria into the circulation. Choice C rationale An electrolyte panel measures substances like sodium (135 to 145 mEq/L) and potassium (3.5 to 5.0 mEq/L). These are essential for monitoring the patient's overall metabolic status and cardiac rhythm stability, especially if they are receiving diuretics or have heart failure secondary to valvular damage. However, electrolytes do not provide any information regarding the presence or absence of a bacterial infection. Therefore, they cannot be used to evaluate how well an antibiotic is working. Choice D rationale Liver function tests (LFTs) measure enzymes such as ALT and AST to assess for hepatic injury. While some intravenous antibiotics used for long-term endocarditis treatment can be hepatotoxic, requiring the nurse to monitor these values for safety, they do not track the progress of the infection itself. Normal ALT ranges are 4 to 36 U/L. Monitoring LFTs is about managing the side effects of the therapy rather than measuring the therapeutic efficacy against the bacteria.