Chemotherapeutic agents often produce a degree of myelosuppression including leukopenia. Leukopenia does not present immediately but is delayed several days or weeks because:

Leukopenia does not present immediately after chemotherapy because time is required to clear circulating cells before the effect on precursor cell maturation in the bone marrow becomes evident. Leukopenia is characterized by an abnormally low white blood cell count. The correct answer is D because the white cell count is not immediately affected by chemotherapy. Choices A, B, and C are incorrect as they pertain to red blood cells (hemoglobin and hematocrit), which are not directly related to the delayed onset of leukopenia.