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Large Red Blood Cells & Normal B12

author image Matthew Fox, MD
Dr. Matthew Fox graduated from the University of California with a Bachelor of Arts in molecular, cell and developmental biology and received a M.D. from the University of Virginia. He is a pathologist and has experience in internal medicine and cancer research.
Large Red Blood Cells & Normal B12
Fatigued woman with her head in her hands Photo Credit: Jupiterimages/Stockbyte/Getty Images

Red blood cells are the most abundant type of blood cell. They carry oxygen through the body from the lungs to the tissues. A low red blood cell count is called anemia. There are several ways to classify anemia. One way is by the size of individual red blood cells. Macrocytic anemia refers to large red blood cells that are few in number. Low levels of vitamin B-12 is a common cause of this type of anemia, but if the vitamin B-12 level is normal, there are other potential causes to look into. Consult with a physician for the diagnosis and management of macrocytic anemia.

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A finding of large red blood cells and normal vitamin B-12 levels points to several possibilities. Alcoholism may create large red blood cells. Low folate levels and some drugs such as methotrexate, used to treat some cancers or rheumatic or immune conditions, interfere with folate metabolism and may cause the condition. Folate, another B vitamin, and vitamin B-12 are both involved in some of the same chemical reactions required to make normal sized red blood cells. Therefore, low levels of either of these B vitamins can lead to large red blood cells. In addition, low thyroid hormone levels, liver disease, bone marrow disorders and pregnancy are other causes of large red blood cells with normal B-12 levels..

Signs and Symptoms

Macrocytic anemia may not produce noticeable symptoms. The condition may create weakness, fatigue and pale skin. Underlying causes of macrocytic anemia may produce other symptoms, such as an increased tendency to bleed in some alcoholics due to damage to the liver, which normally produces proteins to help with blood clotting.


Blood tests confirm a diagnosis of macrocytic anemia. These studies measure the concentration of red cells in the blood, their size, variability, volume and other factors. Determining the cause of the anemia takes into account the person's medical history, including medical conditions and medications, social habits such as alcohol use, a physical exam and other laboratory or imaging studies.


The treatment of macrocytic anemia typically involves addressing the underlying cause. If low folate is found to be the cause of the macrocytic anemia, folate supplementation often follows. Alternatively, if low thyroid hormone levels are the cause, thyroid hormones are administered. If a person is alcoholic, medically supervised alcohol cessation and treatment for any nutrient deficiencies is in order.

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  • Harrison’s Principles of Internal Medicine; Anthony S Fauci et al.; 2008
  • Robbins and Cotran Pathologic Basis of Disease; Vinay Kumar et al.; 2009
  • Physiology; Linda S.Costanzo; 2008
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