Reasons for a Low Blood Count

The bone marrow produces and releases red blood cells, or RBCs, into the bloodstream. RBCs remain in the circulation for approximately four months before replacement with new blood cells. A normal red blood cell count depends on a matched balance between production and loss. Abnormal losses through bleeding or premature destruction, or decreased red blood cell production can cause a low blood count–a condition known as anemia.

Further Reading:
Low TSH Levels: Symptoms, Causes & What to Do
Low HGB and HCT: What does it Mean in Blood Test

Blood Loss

Depletion of red blood cells through significant bleeding may lead to anemia. Acute hemorrhages can occur with trauma or ruptured blood vessels. More commonly, blood loss occurs through chronic or repetitive bleeding. The gastrointestinal tract proves a frequent site of chronic bleeding. Drs. David Dugdale III and George Longstreth note in a Medline Plus Medical Encyclopedia entry that possible causes of gastrointestinal bleeding include peptic ulcer disease, Crohn’s disease, stomach and colorectal cancer, celiac disease, ulcerative colitis, esophageal varices, hemorrhoids and portal hypertensive gastropathy. Among women, heavy menstrual bleeding may also cause significant blood loss leading to anemia. Chronic bleeding typically depletes body iron stores, which further exacerbates the anemia due to blood loss.

Inadequate Bone Marrow Production

Inadequate bone marrow production of red blood cells stands as a significant cause of anemia. Most commonly, inadequate red blood cell output from the bone marrow results from deficiencies in substances required for red blood cell production. Iron is an essential component of red blood cells; insufficient iron causes iron deficiency anemia, a common disorder among women of childbearing age and young children. The National Heart, Lung and Blood Institute notes that vitamin B12 is also essential for red blood cell production. Insufficient vitamin B12 leads to pernicious anemia, also known as megaloblastic anemia.

Genetic and acquired disorders of the bone marrow cells that give rise to red blood cells typically leads to markedly reduced blood cell production. Inherited forms of this condition, termed aplastic anemia, include Diamond-Blackfan anemia, Shwachman-Diamond syndrome and Fanconi anemia. According to the National Heart, Lung and Blood Institute, acquired causes of aplastic anemia include radiation therapy, chemotherapy, toxin exposure, HIV, cytomegalovirus and certain autoimmune diseases.

Decreased RBC Survival

Disorders that cause decreased red blood cell survival in the circulation typically lead to a state of chronic anemia. Sickle cell disease proves a classic form of this type of anemia. The Centers for Disease Control and Prevention explains that people with sickle cell disease possess an inherited genetic defect, which causes misshapen red blood cells with a significantly shortened circulatory lifespan. The bone marrow cannot keep up with the rapid destruction of the sickled red blood cells, and chronic anemia results. The genetic disorders termed the thalassemias also cause malformed red blood cells leading to premature destruction and chronic anemia.

About this Author

Tina Andrews has been a medical writer and editor since 2000. She has published in “Cancer,” “Ethnicity & Disease” and “Liver Health Today” and was formerly a medical officer with the Centers for Disease Control and Prevention. Andrews holds a Doctor of Medicine degree and a Bachelor of Arts in chemistry.