Microcytic anaemia is any of several types of anaemia characterized by small red blood cells (called microcytes). The normal mean corpuscular volume (abbreviated to MCV on full blood count results, and also known as mean cell volume) is approximately 80–100 fL. When the MCV is <80 fL, the red cells are described as microcytic and when >100 fL, macrocytic (the latter occur in macrocytic anemia). The MCV is the average red blood cell size.
In microcytic anaemia, the red blood cells (erythrocytes) contain less hemoglobin and are usually also hypochromic, meaning that the red blood cells appear paler than usual. This can be reflected by a low mean corpuscular hemoglobin concentration (MCHC), a measure representing the amount of hemoglobin per unit volume of fluid inside the cell; normally about 320–360 g/L or 32–36 g/dL. Typically, therefore, anemia of this category is described as "microcytic, hypochromic anaemia".
Typical causes of microcytic anemia include:
- Iron deficiency anemia, by far the most common cause of anemia in general and of microcytic anemia in particular
- Sideroblastic anemia. Very rare. In congenital sideroblastic anemia the MCV (mean corpuscular volume) is either low or normal. In contrast, the MCV is usually high in the much more common acquired sideroblastic anemia.
- Iron deficiency anemia
- Anemia of chronic disease, (aso known as anemia of inflammation) although this can also be normocytic. Microcytic anemia has been discussed by Weng et al.
- Lead poisoning – very rare.
- Hyperthyroidism – very rare.
- Vitamin B6 (pyridoxine) deficiency – very rare.
There are five main causes of microcytic anemia forming the acronym TAILS. Thalassemia, anemia of chronic disease, iron deficiency, lead poisoning and congenital sideroblastic anemia. Only the first three are common in most parts of the world. In theory, these three can be differentiated by their red blood cell (RBC) morphologies. Anemia of chronic disease shows unremarkable RBCs, iron deficiency shows anisocytosis, anisochromia and elliptocytosis, and thalassemias demonstrate target cells and coarse basophilic stippling. In practice though elliptocytes and anisocytosis are often seen in thalassemia and target cells occasionally in iron deficiency. All three may show unremarkable RBC morphology. Basophilic stippling is one morphologic finding of thalassemia which does not appear in iron deficiency or anemia of chronic disease. The patient should be in an ethnically at risk group and the diagnosis is not confirmed without a confirmatory method such as hemoglobin HPLC, H body staining, molecular testing or another reliable method. Coarse basophilic stippling occurs in other cases as seen in Table 1.
- Iolascon A, De Falco L, Beaumont C (January 2009). "Molecular basis of inherited microcytic anemia due to defects in iron acquisition or heme synthesis". Haematologica. 94 (3): 395–408. doi:10.3324/haematol.13619. PMC 2649346. PMID 19181781.
- Weng, CH; Chen JB; Wang J; Wu CC; Yu Y; Lin TH (2011). "Surgically Curable Non-Iron Deficiency Microcytic Anemia: Castleman's Disease". Onkologie. 34 (8–9): 456–8. doi:10.1159/000331283. PMID 21934347.
- Ford, J. (June 2013). "Red blood cell morphology". International Journal of Laboratory Hematology. 35 (3): 351–357. doi:10.1111/ijlh.12082. PMID 23480230.