Macrocytic anaemia

The term macrocytic is from Greek words meaning 'large cell'. A macrocytic class of anemia is an anemia (defined as blood with an insufficient concentration of hemoglobin) in which the red blood cells (erythrocytes) are larger than their normal volume. The normal erythrocyte volume in humans is about 80 to 100 femtoliters (fL= 10−15 L). In metric terms the size is given in equivalent cubic micrometers (1 μm3 = 1 fL). The condition of having erythrocytes which (on average) are too large, is called macrocytosis. In contrast, in microcytic anemia, the erythrocytes are smaller than normal.Megaloblastic anemias represent a type of macrocytic anemia characterized by certain morphologic abnormalities noted on a peripheral blood smear examination. These abnormalities include the presence of enlarged oval shaped red blood cells (macroovalocytes) and hypersegmented neutrophils (defined as a neutrophil with six or more lobes). Hypersegmented neutrophils may be seen in the absence of macroovalocytes as hypersegmentation of neutrophils is an early sign of megaloblastic anemia and may precede the appearance of macroovalocytes; they may also be seen in other anemias (e.g., iron deficiency anemia) and thus are suggestive of megaloblastic anemia but not specific for it. An increased red cell distribution width (anisocytosis) also suggests megaloblastosis and is commonly seen in Vitamin B12 deficiency and folic acid deficiency. This type of anemia is caused by impaired DNA synthesis and repair, often from deficient thymidine production. Thiamine responsive megaloblastic anemia syndrome also causes megaloblastic anemia.Several tests can help to elucidate the underlying cause of a person's macrocytic anemia. A peripheral blood smear is often recommended as a first step in the evaluation to determine if the macrocytic anemia has megaloblastic features since the causes of megaloblastic and non-megaloblastic macrocytic anemia differ and making this distinction can narrow the list of differential diagnoses.Macrocytic anemias have several causes but with the implementation of folic acid fortification in North America, folic acid deficiency has become a rare cause of megaloblastic macrocytic anemia in that part of the world. In this region, Vitamin B12 deficiency is a far more common cause of megaloblastic macrocytic anemia. In countries that have not put such practices into place-including most European nations-folic acid deficiency remains a common cause of macrocytic anemia.