Which of the following would be a common laboratory finding for a patient receiving chemotherapy?

In patients undergoing chemotherapy, a common laboratory finding is a low white blood cell count, known as leukopenia. Chemotherapy is designed to target rapidly dividing cells, which includes not only cancerous cells but also normal cells in the bone marrow that produce white blood cells. This can lead to a decreased immune response, making patients more susceptible to infections and requiring careful monitoring of their blood counts during treatment.

Other options like high hematocrit and high platelet count are not typical outcomes of chemotherapy, as the treatment often suppresses bone marrow function. Similarly, a low prothrombin time is not usually associated with chemotherapy; instead, some treatments may affect clotting factors and could lead to a normal or even high prothrombin time depending on the patient's overall status and other factors. Thus, low white blood cell count stands out as the most pertinent lab finding in this context.