Chemotherapy destroys rapidly dividing cells, a characteristic of cancer cells. However, red blood cells, white blood cells, and platelets also divide rapidly and are frequently damaged by chemotherapy. Your red blood cell count, white blood cell count, and platelet count may all go down. Your doctor monitors these counts to determine the toxicity of treatment and to predict your risk for complications, as well as to plan future therapy. For more information, see section on Understanding and Monitoring Your Blood Counts.