Blood is composed of a number of cell types, each of which performs distinct functions throughout the body. Red blood cells, the most numerous cell type in the blood, contain hemoglobin, which carries oxygen from the lungs to all the tissues of the body. White blood cells help make up the immune system and fight off infection and disease. Platelets, the smallest cells, help control blood clotting to prevent uncontrolled bleeding. Several diseases or conditions impact white blood cells and platelets, leading to immunodeficiency and irregular bleeding.
HIV Infection
One potential cause of a low white blood cell and platelet count is infection with the human immunodeficiency virus, or HIV. HIV works by entering white blood cells and hijacking cellular machinery to create several more copies of the HIV virus within the white blood cell. After the virus has replicated, it signals for the white blood cell to burst open, killing the cell and releasing viruses into the bloodstream to infect other white blood cells. As the infection progresses, more and more white blood cells are killed, leading to very low white blood cell counts.
HIV infection also leads to a decrease in platelet cell numbers, indicates Merck. Upon HIV infection, the body's immune system produces proteins called antibodies, which circulate throughout the body and target cells or microbes for destruction. During HIV infection, antibodies released into the bloodstream target platelets for destruction, leading to a decrease in platelet cell numbers.
Aplastic Anemia
Another cause of decreased white blood cell and platelet cell count is aplastic anemia, a disorder caused by damage to bone marrow. Blood cells within the body constantly turn over, so bone marrow must continually proliferate to give rise to enough blood cells to replace any destroyed cells. Aplastic anemia develops when the bone marrow cells cannot provide enough new blood cells. It can develop if bone marrow cells become damaged and die or if bone marrow cells dysfunction and do not proliferate properly. Aplastic anemia decreases white blood cell, platelet and red blood cell counts. The disease can be treated with blood transfusions or drugs to stimulate bone marrow cell proliferation, reports the University of Maryland Medical Center.
Chemotherapy Treatment
Some cancer treatments, such as chemotherapy, can decrease white blood cell and platelet cell counts in the blood. Chemotherapy drugs damage the cells' DNA, leading to cell death, or inhibit essential cellular pathways required for the cell to sustain itself. These drugs do not selectively kill cancer cells, but instead target populations of proliferating cells throughout the entire body, including bone marrow cells. During chemotherapy treatment, damage to bone marrow cells decreases white blood cells and platelets, as well as red blood cell count. Patients receiving chemotherapy treatment must be monitored for blood cell counts, and an extreme decrease in blood cells may require temporary cessation of treatment. The effect of chemotherapy on blood cell counts is temporary, and blood cells increase again after treatment has stopped.
