People with megaloblastic anemia have abnormal red blood cells because they have a deficiency in either folic acid or vitamin B12. The red blood cells are macrocytic, or abnormally large, due to a problem making DNA. If they are anemic because of a vitamin B12 deficiency, it can be years before they have any symptoms because liver stores of vitamin B12 usually last for years.
What is Anemia?
The normal range of red blood cells is 3,800,000 to 5,100,000 per microliter for a woman and 4,300,000 to 5,700,000 per microliter for a man. People with anemia have fewer red blood cells circulating in their bloodstream, have a problem with the hemoglobin in their red blood cells or have both problems. They become anemic when many of their red blood cells are being destroyed, they are hemorrhaging, slowly bleeding for quite some time or have abnormalities in the production of their red blood cells, as explained by Elizabeth Corwin, Ph.D. in "Handbook of Pathophysiology."
What is Megaloblastic Anemia?
People with megaloblastic anemia are anemic because they have abnormalities in the production of their red blood cells. They have a deficiency of either folic acid or vitamin B12, writes Morey Blinder, M.D. in "The Washington Manual of Medical Therapeutics." The body uses folic acid to make DNA and RNA, while vitamin B12 works with folic acid and also makes myelin for the nerves. A deficiency of either vitamin leads to problems making DNA. Because blood cells divide so rapidly and, therefore, especially need DNA, the red blood cells are abnormal.
Causes of a B12 Megaloblastic Anemia
The liver usually stores enough vitamin B12 to last for years, so signs of a deficiency can take years to develop. In "The Washington Manual of Medical Therapeutics," Dr. Blinder writes that a deficiency may be due to pernicious anemia, bacteria, parasites, inflammation or surgical removal of part of the small intestines, removal of part or all of the stomach or abnormalities in the pancreas. In pernicious anemia, the parietal cells of the stomach that secrete a protein called intrinsic factor have been destroyed. Intrinsic factor is necessary to absorb vitamin B12.
Folic Acid vs. Vitamin B12
Both a folic acid deficiency and a B12 deficiency cause abnormal megaloblastic red blood cells that are also macrocytic, or too large. Looking at the red blood cells on a slide in the lab will not show whether the disorder is due to a deficiency of folic acid or B12. Taking folic acid will not treat a vitamin B12 deficiency or vice-versa. Since B12 makes myelin that covers part of the nerves, people with a B12 deficiency will have neurological problems, as described by Alan Lichtin, M.D. of the Cleveland Clinic in "The Merck Manual for Healthcare Professionals."
Evaluation and B12 Treatment
Dr. Blinder explains in "The Washington Manual of Medical Therapeutics" that the evaluation should include measuring the levels of vitamin B12 and folate. If still undecided, a physician can measure the levels of methylmalonic acid and homocysteine. Both of these substances are increased in a B12 deficiency, while only homocysteine increases in a folic acid deficiency. A Schilling test can determine if people are deficient in intrinsic factor. People are then treated with vitamin B12.
References
- "Handbook of Pathophysiology"; Elizabeth Corwin, MSN, Ph.D., FNP; 2000
- The Merck Manual for Healthcare Professionals: Megaloblastic Macrocytic Anemias
- "The Washington Manual of Medical Therapeutics"; Gopa Green, M.D., Ian Harris, M.D., Grace Lin, M.D., Kyle Moylan, M.D.; 2004
