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What is megaloblastic anemia?

Megaloblastic anemia is a form of anemia characterized by very large red blood cells and a decrease in the number of those cells. Anemias are blood disorders that occur when the body has fewer red blood cells than normal. Red blood cells carry oxygen throughout the body using a protein called hemoglobin. If there aren’t enough of these cells or this protein, anemia results.

Usually, megaloblastic anemia is due to acquired deficiency in vitamin B12 or folic acid. The deficiency can be related to inadequate dietary intake of these B vitamins or poor intestinal absorption. Rarely, megaloblastic anemias are the result of medications or inherited defects in the transport/metabolism of vitamin B12 or folic acid.

Pernicious anemia

Pernicious anemia is a type of megaloblastic anemia in which the body isn’t able to absorb vitamin B12 due to a lack of intrinsic factor in stomach secretions. Intrinsic factor is needed for the body to absorb vitamin B12.

For all types of megaloblastic anemia, in addition to the red blood cells being large, the inner contents of each cell are not completely developed. This malformation causes the bone marrow to produce fewer cells, and sometimes the red blood cells die earlier than the 120-day life expectancy.

How we care for megaloblastic anemia

Children and young adults with megaloblastic anemia are treated through Dana-Farber/Boston Children's Cancer and Blood Disorders Center, an integrated pediatric hematology and oncology partnership between Dana-Farber Cancer Institute and Boston Children's Hospital.

Our joint Blood Disorders Center brings together world-renown pediatric hematology specialists and support staff from across Dana-Farber/Boston Children's, including pediatric hematologist/oncologists, hematopathologists, hematology nurse practitioners, social workers and designated hematology patient coordinators. For many appointments and certain procedures, your child can also receive care at one of Boston Children's satellite offices.

Megaloblastic Anemia | Symptoms & Causes

What are the symptoms of megaloblastic anemia?

Each child may experience symptoms of megaloblastic anemia differently. Some children with pernicious anemia do not have symptoms, or they may be mild. Common symptoms of the condition include:

  • pale skin, lips, and hands
  • decreased appetite
  • irritability
  • lack of energy or fatigue
  • diarrhea or constipation
  • difficulty walking (Vitamin B12 specific)
  • numbness or tingling in hands and feet (Vitamin B12 specific)
  • smooth and tender tongue
  • weak muscles (Vitamin B12 specific)
  • lightheadedness upon standing or exertion
  • difficulty concentrating
  • shortness of breath (primarily during exercise)
  • swollen, red tongue
  • bleeding gums

It is important to understand that some symptoms of megaloblastic anemia may resemble those of other more common medical problems or other blood disorders. Because some of these symptoms can also point to other conditions, and because anemia itself can be a symptom of another medical problem, it’s important to have your child evaluated by a qualified medical professional for an accurate diagnosis and prompt treatment.

What causes megaloblastic anemia?

Megaloblastic anemia most commonly results from an acquired nutritional deficiency or inability to absorb nutrients. Common causes include:

  • dietary deficiency of folic acid
  • dietary deficiency of vitamin B12
  • certain diseases of the lower digestive tract, including celiac disease
  • atrophic gastritis
  • an autoimmune attack on the stomach cells that produce the binding partner of Vitamin B12 that allows it to be absorbed further down the intestine
  • medication-induced folic acid deficiency

In rare cases, megaloblastic anemia is the result of inherited problems. These can include thiamine-responsive megaloblastic anemia syndrome (TRMA) — a rare inherited megaloblastic anemia characterized by megaloblastic anemia, sensorineural hearing loss, and diabetes mellitus; congenital (inherited) vitamin B12 deficiency which can be the result of inherited deficiency of intrinsic factor or the receptor in the intestines (Imerslund-Grasbeck syndrome), or other vitamin B12 transporters (Transcobalamin deficiency); or inherited congenital folate malabsorption is a genetic problem in which infants cannot absorb folic acid in their intestines. This requires early intensive treatment to prevent long-term problems, including significant intellectual disabilities.

Megaloblastic Anemia | Diagnosis & Treatments

How is megaloblastic anemia diagnosed?

Your child's doctor may suspect megaloblastic anemia after taking a complete medical history and physical examination of your child. Megaloblastic anemia is diagnosed through a physical exam and other tests, including:

  • complete blood count
  • reticulocyte count
  • blood tests to measure of vitamin B12, methylmalonic acid (MMA), or homocysteine levels
  • blood tests to detect the antibodies toward intrinsic factor or the cells that produce it
  • a bone marrow exam may be necessary if the diagnosis is unclear.

There may be other diagnostic tests that your doctor will discuss with you depending on your child's individual situation. After we complete all necessary tests, our experts meet to review and discuss what they have learned about your child's condition. Then we will meet with you and your family to discuss the results and outline the best possible treatment options.

What are the treatment options for megaloblastic anemia?

Megaloblastic anemia treatment typically includes:

  • replacing any nutritional deficiencies through changes in diet 
  • an oral dietary folic acid supplement regimen
  • injections of vitamin B12 once a month
  • possibly addressing the absorption problem in the digestive tract

Of course, your child's team of doctors will help determine the best approach for your child's unique situation, based on a number of factors including:

  • the underlying cause of the megaloblastic anemia
  • your child's age, overall health, and medical history
  • the severity of the disease
  • your child's tolerance for certain medications, procedures, or therapies
  • how your child's doctors expect the disease to progress
  • your opinion and preferences

Megaloblastic Anemia | Programs & Services