Megaloblastic macrocytic anemia
Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. There are many types of anemia.
Vitamin B12 deficiency anemia is a low red blood cell count due to a lack (deficiency) of vitamin B12.
This picture shows large, dense, oversized, red blood cells (RBCs) that are seen in megaloblastic anemia. Megaloblastic anemia can occur when there is a deficiency of vitamin B-12.
This image shows a large polymorphonuclear leukocyte (PMN) with multiple discretely-identifiable nuclear lobes. It can be seen in megaloblastic anemias. Normal PMN's have less than or equal to 5 lobes.
Causes
Your body needs vitamin B12 to make red blood cells. In order to provide vitamin B12 to your cells:
- You must eat foods that contain vitamin B12, such as meat, poultry, shellfish, eggs, fortified breakfast cereals, and dairy products.
- Your body must absorb enough vitamin B12. A special protein, called intrinsic factor, helps your body do this. This protein is released by cells in the stomach.
A lack of vitamin B12 may be due to dietary factors, including:
- Eating a strict vegetarian diet
- Poor diet in infants
- Poor nutrition during pregnancy
Certain health conditions can make it difficult for your body to absorb enough vitamin B12. They include:
- Alcohol use
- Crohn disease, celiac disease, infection with the fish tapeworm, or other problems that make it difficult for your body to digest foods
- Pernicious anemia, a type of vitamin B12 anemia that occurs when your body destroys cells that make intrinsic factor
- Surgery that removes certain parts of your stomach or small intestine, such as some weight-loss surgeries
- Taking antacids and other heartburn medicines for a long period of time
- Abuse of "laughing gas" (nitrous oxide)
Symptoms
You may not have symptoms. Symptoms may be mild.
Symptoms can include:
- Diarrhea or constipation
- Fatigue, lack of energy, or lightheadedness when standing up or with exertion
- Loss of appetite
- Pale skin
- Feeling irritable
- Shortness of breath, mostly during exercise
- Swollen, red tongue or bleeding gums
If you have low vitamin B12 level for a long time, you can have nerve damage. Symptoms of nerve damage include:
- Confusion or change in mental status (dementia) in severe cases
- Problems concentrating
- Psychosis (losing contact with reality)
- Loss of balance
- Numbness and tingling of hands and feet
- Hallucinations
Exams and Tests
The health care provider will perform a physical exam. This may reveal problems with your reflexes.
Tests that may be done include:
- Complete blood count (CBC)
- Reticulocyte count
- Lactate dehydrogenase (LDH) level
- Serum bilirubin level
- Vitamin B12 level
- Methylmalonic acid (MMA) level
- Serum hom*ocysteine level (amino acid found in blood)
Other procedures that may be done include:
- Esophagogastroduodenoscopy (EGD) to examine the stomach and small intestine
- Bone marrow biopsy if the diagnosis is not clear
Treatment
Treatment depends on the cause of B12 deficiency anemia.
The goal of treatment is to increase your vitamin B12 level.
- Treatment may include a shot of vitamin B12 once a month. If you have a very low level of B12, you may need more shots in the beginning. It is possible you may need shots every month for the rest of your life.
- Some people may respond to treatment by taking vitamin B12 supplements by mouth.
Your provider will also recommend that you eat a variety of foods.
Outlook (Prognosis)
People with this type of anemia often do well with treatment.
Long-term vitamin B12 deficiency can cause nerve damage. This may be permanent if you do not start treatment within 6 months of when your symptoms begin.
Vitamin B12 deficiency anemia most often responds well to treatment. It will likely get better when the underlying cause of the deficiency is treated.
Possible Complications
A woman with a low B12 level may have a false positive Pap smear. This is because vitamin B12 deficiency affects the way certain cells (epithelial cells) in the cervix look.
When to Contact a Medical Professional
Call your provider if you have any of the symptoms of anemia.
Prevention
You can prevent anemia caused by a lack of vitamin B12 by eating a well-balanced diet.
Shots of vitamin B12 can prevent anemia if you've had a surgery known to cause vitamin B12 deficiency.
Early diagnosis and prompt treatment can reduce or prevent complications related to a low vitamin B12 level.
References
Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 39.
Means RT. Approach to the anemias. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 149.
Perez DL, Murray ED, Forester BP, Price BH. Depression and psychosis in neurological practice. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 10.
Version Info
Last reviewed on: 1/25/2022
Reviewed by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
