Many cell types within the blood perform specialized functions throughout the body. White blood cells help make up the immune system and protect the body from infection. Red blood cells bind to oxygen from the lungs and distribute oxygen to tissues throughout the body. Platelets respond to blood vessel injury by forming a clot to control bleeding. Low blood cell counts can lead to a number of diseases and disorders, and the low cell counts can result as a side effect of therapeutics or indicate a harmful underlying disorder.
Aplastic Anemia
Aplastic anemia is a condition that develops when bone marrow cells can't produce enough new blood cells. Normally, bone marrow contains a population of blood stem cells, which continually divide and give rise to cells that eventually mature into functional blood cells. Patients with aplastic anemia have damaged bone marrow, so the cells can't proliferate properly and therefore do not give rise to mature cells, reports the National Heart and Lung Institute. The condition may have a genetic basis, with inherited mutations leading to bone marrow failure or acquired as a result of bone marrow injury. Aplastic anemia can be treated with a bone marrow transplant.
HIV Infection
In some cases, low blood cell numbers affecting one blood cell type can indicate a targeted disease or infection, such as HIV infection. The HIV virus infects white blood cells and progressively lowers white blood cell counts. Once the virus enters the white blood cell, the virus replicates its genetic material within the white blood cells and instructs the cell to make thousands of copies of the virus. Once the virus has replicated within the cell, the white blood cell explodes, releasing more virus into the bloodstream--where it can infect more white blood cells. Over time, patients with HIV infection develop AIDS--acquired immunodeficiency syndrome--as a result of low white blood cell counts. HIV medications that prevent HIV infection or replication can help increase levels of white blood cells over time.
Cancer Therapy
Many cancer therapies, such as chemotherapy treatment, target rapidly proliferating cells throughout the body to kill cancer cells. Normal bone marrow cells, which continually proliferate, are targeted by chemotherapy. This leads to an overall decrease in functional bone marrow cells, giving rise to new blood cells. As a result, patients undergoing chemotherapy often experience a temporary decrease in blood cell counts, reports MayoClinic.com. Blood cell counts increase after cessation of chemotherapy treatment.
