Megaloblastic Anemia: What It Is, Causes, and How It Is Detected

A blood test sometimes includes a line about large red blood cells, and with it comes a diagnosis that sounds frightening. In fact, it reflects understandable mechanisms: the body lacks vitamin B12 or folate, and blood cells mature incorrectly. Let's go through this calmly, without scare stories.

What megaloblastic anemia is

Megaloblastic anemia is a condition in which, due to a lack of vitamin B12 or folate, the body produces abnormally large red blood cells that cannot function normally. In the bone marrow, many large immature red blood cell precursors — megaloblasts — accumulate. Red blood cells carry oxygen using hemoglobin, so with anemia, tissues receive less oxygen. One variant is pernicious anemia, when the intestine cannot properly absorb vitamin B12.

How macrocytic anemia differs from megaloblastic anemia

Macrocytic anemia is a description of what is seen in a test: red blood cells are larger than usual. Megaloblastic anemia is a more precise explanation of the cause: a disruption in cell maturation due to B12 or folate deficiency. In other words, macrocytosis is the picture, and the megaloblastic mechanism is what underlies it. The doctor assesses the test as a whole together with symptoms, not a single line.

Why megaloblastic anemia occurs: main causes

One cause of B12 deficiency is pernicious anemia: the immune system attacks healthy stomach cells, and the vitamin is not absorbed from food. Vitamin shortages in the diet also occur — for example, with vegan eating without B12 supplements or with a long monotonous diet. Some medications, including anticonvulsants and proton pump inhibitors, affect the absorption of these vitamins. Other causes include atrophic gastritis, stomach surgery, intestinal diseases with impaired absorption, and tapeworm infestation. B12 and folate deficiency is more common in older people: in about 1 in 10 people aged 75 and older and in 1 in 20 aged 65–74.

What symptoms may occur with this anemia

Symptoms vary and are not always pronounced. These include marked fatigue, lack of energy, tingling in the hands and feet, a sore red tongue, mouth sores, muscle weakness, and vision problems. Psychological manifestations may also occur — from mild depression or anxiety to confusion and problems with memory and comprehension. In pernicious anemia, diarrhea or constipation, nausea, loss of appetite, pale skin, shortness of breath on exertion, heartburn, a swollen red tongue, or bleeding gums occur. Some of these problems also occur without anemia — with the vitamin deficiency itself.

What a blood test shows and how the diagnosis is made

The doctor starts with an examination and a complete blood count. Next, vitamin B12, reticulocytes, lactate dehydrogenase, bilirubin, methylmalonic acid, and homocysteine levels may be ordered, as well as antibodies to intrinsic factor or to the cells that produce it. The diagnosis is made based on the combination of results and symptoms.

• Complete blood count
• Vitamin B12 level
• Reticulocytes, LDH, bilirubin
• Methylmalonic acid and homocysteine
• Antibodies to intrinsic factor

Possible complications and when a doctor is needed

If the deficiency lasts a long time, the nervous system may be affected: numbness, tingling, impaired balance, confusion, and problems with concentration appear. Without treatment, irreversible death of nerve cells is possible — damage may remain permanent if treatment is not started within 6 months after symptoms appear. Other complications include heart problems, temporary infertility, and pregnancy complications. People with pernicious anemia have a higher risk of polyps and stomach cancer, and fractures. A doctor should be consulted for any suspicious symptoms — early diagnosis helps reduce the risk of complications.

Anemia itself is not a reason to call an ambulance; 103/112 — for signs of a life-threatening condition, such as a stroke or heart attack.

This is reference material, not a substitute for a doctor's consultation: if vitamin deficiency is suspected, it is better to discuss the tests with your doctor.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer