Inadequate generation of red blood cells, platelets or white blood cells by the bone marrow can cause a low blood count. This can occur due to certain bone marrow diseases such as paroxysmal nocturnal hemoglobinuria, aplastic anemia and myelodysplastic syndromes, bleeding, and abnormal hemoglobin formation or red blood cell shape. Other causes include certain gastrointestinal conditions, viruses and vitamin deficiencies, as the Aplastic Anemia & MDS International Foundation reports.
A low blood count indicates that the number of red blood cells, platelets and white blood cells in the blood is low, according to the Aplastic Anemia & MDS International Foundation.
A low red blood cell count indicates the presence of anemia and can result from excessive bleeding during menstruation, ulcers in the stomach, cancer in the colon and inflammatory bowel disease. Deficiencies of vitamin B12 and folic acid cause pernicious anemia. Spleen removal, thalassemia, sickle cell disease, reactions to certain drugs and chemicals, Addison's disease, and lead poisoning can also lower an individual's red blood cell count, as WebMD explains.
A low white blood cell count occurs in patients undergoing chemotherapy and as a reaction to some medications. An enlarged spleen, lupus, viral infections, AIDS, alcoholism, malaria, aplastic anemia and Cushing's syndrome are other causes, as indicated by WebMD.
Platelet counts are low in patients who suffer from idiopathic thrombocytopenic purpura and in pregnant women. Other conditions that affect platelet generation and destruction as well as an enlarged spleen are other possible causes, according to WebMD.