A nurse is reviewing the laboratory data of a client who is receiving filgrastim. Which of the following laboratory values should the nurse monitor to evaluate the effectiveness of the treatment?

A. INR (International Normalized Ratio) is used to monitor blood clotting and is not relevant to evaluating the effectiveness of filgrastim. Filgrastim is used to stimulate the production of white blood cells, so monitoring INR would not provide useful information about its effectiveness. B. WBC count (White Blood Cell count) is the primary laboratory value to monitor when evaluating the effectiveness of filgrastim. Filgrastim is a granulocyte colony-stimulating factor that promotes the production of neutrophils, a type of white blood cell. An increase in WBC count indicates that the treatment is effective. C. Potassium level is important for overall health but is not directly related to the effectiveness of filgrastim. Monitoring potassium levels is not necessary for assessing the response to filgrastim therapy. D. BUN (Blood Urea Nitrogen) measures kidney function and is not relevant to evaluating the effectiveness of filgrastim. Monitoring BUN levels would not provide information about the response to filgrastim treatment.