Macrocytosis is a blood disorder characterized by the presence of abnormally large red blood cells in the circulation. In the majority of cases, macrocytosis is linked to a defect in cell division of red blood cell precursors in the bone marrow. Its incidence in hospitalized adults varies between 1% and 3,6% but it can also affect children. Among the most common causes are deficiencies or absorption defects of vitamins B9 and B12.

Definition of macrocytosis

Macrocytosis is a blood disorder characterized by the presence of abnormally large red blood cells in the circulation.

In adults, macrocytosis is effective when the mean globular volume (MCV) – the division of the volume of red blood cells in relation to the total volume of blood by the number of red blood cells per cubic millimeter of blood – is greater than 100 femtoliter (fL ), or a diameter greater than 9 microns. In newborns, the MCV is a little higher (105 to 125 fL) for a few weeks and then decreases. In children from two months to 12 years of age, macrocytosis is effective if the MCV is greater than 95 fL.

In the majority of cases, macrocytosis is linked to a defect in cell division of red blood cell precursors in the bone marrow.

Types de macrocytoses

There is only one type of macrocytosis.

Causes of macrocytosis

The causes of macrocytosis are various:

• Chronic alcoholism;
• Liver failure (hepatitis, cirrhosis);
• Hypothyroidism: the thyroid does not secrete enough thyroid hormones;
• Taking certain drugs or toxicants: anticancer chemotherapy, antiretrovirals, sulfonamides, colchicine, neomycin, antacids, barbiturates, nitrogen oxide, oral contraceptives…;
• The defect in the production of red blood cells, acquired or constitutional, by the bone marrow: aplastic anemia (insufficient production of red blood cells) and Blackfan-Diamond anemia (rare genetic disease), myelodysplastic syndromes (MDS), myelofibrosis (type of leukemia) chronic);
• Deficiencies in vitamins B12 or folate (products derived from folic acid or vitamin B9 involved in the renewal of the body’s cells): megaloblastic anemias (deficiency of vitamin B12 or folic acid), deficiencies in intake or increased consumption (childhood, pregnancy, chronic hemolytic anemias, cancers in the proliferating phase, etc.), lack of intestinal absorption, anti-folic drugs, Biermer’s disease, atrophic gastritis, total or partial gastrectomies (removal of the stomach), extreme malnutrition, etc.;
• Invasion of the bone marrow by leukemia, lymphoma or metastatic cells.

Note that 5% of macrocytosis cases present more than one of these combined causes and that 5% of them are of unknown cause.

Diagnostic de la macrocytose

Macrocytosis is diagnosed from a complete blood count (CBC), by measuring the mean blood volume (MCV).

The next step is to look for the cause and further examinations are often essential. Among them :

• Complementary blood tests to measure certain vitamins;
• A possible sample of the bone marrow to check that there is no anomaly in the maturation of red blood cells at this level.

People affected by macrocytosis

The incidence of macrocytosis in hospitalized adults varies between 1% and 3,6% but it can also affect children.

Factors favoring macrocytosis

The factors favoring macrocytosis are:

• Chronic alcoholism;
• Deficiencies in vitamins B12 or folate (B9).

Macrocytic anemia

Only 50 to 60% of macrocytoses present with associated anemia. This anemia, caused by a deficiency in vitamins (B12 and B9), remains asymptomatic for a long time and then quickly becomes severe.

Troubles digestifs

Digestive disorders (epigastric discomfort, diarrhea) often linked to the consequences of a gastrointestinal operation, a clinical malabsorption syndrome or liver cirrhosis or vitamin deficiency, may accompany macrocytosis.

Neurological symptoms

Macrocytosis, when accompanied by neuroanemic syndrome, can lead to deep sensitivity and psychic disturbances.

Other symptoms

• Tired ;
• Pale skin ;
• Increased heart rate;
• Shortness of breath;
• Headache ;
• Dizziness…

Treatment for macrocytosis depends on its cause.

When it follows a deficiency of vitamin B12 or folic acid, patients are treated with injections of vitamin B12 and drugs containing folic acid.

Biermer’s disease, an autoimmune disease causing malabsorption of vitamin B12, requires lifelong treatment associated with gastric monitoring (fibroscopy) every 3 to 4 years.

If the causes of macrocytosis are often difficult to predict, two tips can prevent its occurrence:

• Avoid alcohol;
• Favor a balanced diet to avoid any vitamin deficiency: fruits, green vegetables, organ meats, milk and fermented cheeses for folate (vitamin B9) and meat, eggs, fish and shellfish for the vitamin B12.