Human blood contains three classifications of specialized cells: red blood cells, white blood cells and platelets. The protein hemoglobin, the main component of red blood cells, carries oxygen throughout the body. Medications, conditions and diseases that decrease the number of red blood cells also cause a low level of hemoglobin, defined by MayoClinic.com as less than 135 grams per liter in men and less than 120 grams per liter in women. Many factors that affect red blood cells can also cause a decrease in white blood cells.
Medications
Immature cells, known as stem cells, found in the bone marrow continually produce new blood cells. Because stem cells rapidly grow and divide, they become vulnerable to attack by certain types of medications. Chemotherapy describes the use of toxic drugs to kill cancer cells. Because cancer cells grow rapidly, chemotherapy drugs target rapidly dividing cells. Taking these medications causes stem cells to die, resulting in a decrease in both white blood cells and red blood cells, and therefore hemoglobin.
Doctors utilize drugs classified as antiretroviral drugs to treat the human immunodeficiency virus--HIV, a virus that attacks a specific type of white blood cell. Although antiretroviral therapy inhibits the virus from replicating, therefore reducing the symptoms, it can also cause a decrease in both white blood cells and red blood cells.
Aplastic Anemia
Anemia describes a condition characterized by a low level of red blood cells. Aplastic anemia describes a blood disorder that originates in the stem cells, and doctors sometimes refer to it as bone marrow failure. Aplastic anemia may be inherited or acquired, caused by toxins, chemotherapy or radiation.
In those with aplastic anemia, the stem cells become damaged, inhibiting their ability to produce new blood cells. The resulting decrease in both red blood cells and white blood cells causes symptoms including shortness of breath, dizziness, cold hands and feet, pale skin, chest pain and frequent infections, according to the National Heart Lung and Blood Institute.
Enlarged Spleen
The spleen, an organ located in the left side of the abdomen, filters and destroys old and damaged blood cells, prevents infections by producing mature white blood cells and stores blood. When the spleen becomes enlarged, due to infections, disease or cancer, it fails to perform these vital functions effectively.
An enlarged spleen may filter out normal red blood cells as well as the damaged ones, causing a low level of circulating red blood cells and hemoglobin. Because the enlarged spleen cannot produce mature lymphocytes, a specific type of white blood cell, the resulting low level of white blood cells leaves the patient vulnerable to serious infections.
