Sudden or chronic bleeding, such as gastrointestinal and heavy menstrual bleeding, may cause a low red blood cell or RBC count, according to the American Association for Clinical Chemistry. Iron, vitamin B12 and folate deficiencies may also decrease red blood cell count.
Other conditions that cause low RBC counts include overhydration, pregnancy, kidney disease, leukemia and bone marrow failure, according to MedlinePlus.
Bone marrow is responsible for producing red blood cells, according to the AACC. These blood cells carry oxygen from the lungs to the rest of the body. Red blood cells also escort some carbon dioxide and other metabolic waste from the body through the lungs. Because the typical lifespan of the blood cell is 120 days, bone marrow must continually produce red blood cells that are destroyed by age and other factors.
When the body does not supply enough healthy red blood cells, anemia develops, according to MedlinePlus. At mild levels, some patients develop unusual fatigue, headaches and confusion. As anemia progresses, patients may experience symptoms such as brittle nails, shortness of breath and a desire to eat ice. Once diagnosed with anemia, a physician may recommend nutritional supplements, blood transfusions or erythropoietin, a medication that encourages bone marrow to produce more red blood cells.