There are many possible reasons for a low blood count, and several may coexist in one person. The primary test for blood counts called a complete blood count, or CBC, measures the concentration of red cells, white cells and platelets. A low blood count may refer to low levels of any of these blood cells.
Microcytic Anemia
Microcytic anemia is a common cause of low blood counts. It refers to low erythrocyte counts with smaller than normal cells. Generally microcytic anemias occur from defects in hemoglobin synthesis. The four categories of microcytic anemia include iron deficiency anemia, sideroblastic anemia, thalassemias and anemia of chronic disease. The hemoglobin molecule contains four protein subunits, and a ring structure that carries iron, which is responsible for binding oxygen for transport. In iron deficiency anemia the ring is unable to be fully constructed without iron. The ring is unable to be constructed in sideroblastic anemia as well. Even though iron is available, the body is unable to incorporate it into the ring. This type of anemia can occur from lead poisoning and cancers, among other causes. Thalassemias are inborn defects in synthesis of the hemoglobin protein chains. In anemia of chronic disease, the body creates chemical factors of inflammation such as interleukin 1 and tumor necrosis factor which suppress red blood cell production and the utilization of iron.
Normocytic Anemia
Normocytic anemia is also a common cause of low blood counts. Normocytic anemia stems from increased red blood cell loss or destruction, decreased red cell production, or expansion of the plasma volume. Increased red cell loss occurs from an acute blood loss or an overactive spleen that is trapping too many red cells. Destruction of red cells may stem from the immune system, inherited defects in red cell stability, or mechanical destruction from blood clots in the vessels, for example. Decreased red cell production may be a result of conditions such as bone marrow failure, liver and kidney problems. Also, sideroblastic anemia and anemia of chronic disease can manifest as normocytic anemia. In fact, according to American Family Physician, the most common cause of normocytic anemia is anemia of chronic disease. The third category of normocytic anemia is from the addition of more of the liquid component of blood, called plasma, which dilutes the blood. This occurs during over-hydration or pregnancy.
Macrocytic Anemia
Macrocytic anemias are not as common as normocytic and microcytic anemias, but are nonetheless an important cause of low blood counts. Mild macrocytic anemias, when the red blood cells are slightly larger than normal, may be found in alcoholism. Macrocytic anemias in which the cells are considerably larger than normal, however, are caused by either folate or vitamin B12 deficiency. Folate deficiency is associated mostly with anemia, whereas vitamin B12 deficiency is associated with the anemia plus damage to nerves.
Leukopenia
Low blood counts are not restricted to red blood cells. In leukopenia, the low blood counts are caused by loss of white blood cells. According to MayoClinic.com, one common cause of low white cell counts is destruction of bone marrow cells. This can occur from infection or infiltration of the bone marrow by cancer cells. Drugs such as chemotherapy and radiation treatment may also be culprits. Similarly the white cells can be overwhelmed by infection, drugs or autoimmune disorders.
Thrombocytopenia
Another cause of low cell counts is thrombocytopenia, which refers to having low platelets. Low platelet counts are stem from increased destruction or decreased production. Increased destruction occurring in the blood vessels is classified as intravascular. Causes of intravascular destruction include immune disorders, drugs, infections and blood clots in the vessels. Destruction outside the blood vessels is usually from an overly active spleen. Decreased production is seen in processes that infiltrate the bone marrow, bone marrow failure or alcoholism.
